Vitamins

Encyclopedia of Food and Culture
COPYRIGHT 2003 The Gale Group Inc.

VITAMINS

Water-Soluble and Fat-Soluble Vitamins

Vitamins are among the nutrients found to be essential for life. Unlike other classes of nutrients, vitamins serve no structural function nor do they provide significant energy. Their various uses tend to be highly specific. Common food forms of most vitamins require some metabolic activation into a functional (active) form. Although vitamins share these general characteristics, they show few close chemical or functional similarities. For example, some vitamins function as coenzymes, others function as antioxidants, and two vitamins, A and D, function as hormones.

Fourteen substances are now generally recognized as vitamins. Vitamins are frequently described according to their solubility; they may be either fat-soluble or watersoluble. This method of classification dates back to the history of their discovery as labeled by McCollum as "fatsoluble A" and "water-soluble B."

Other sections in this encyclopedia describe the chemistry, biochemistry, and physiology of the vitamins. This article provides additional information that is focused on dietary requirements, upper levels (to avoid toxicity from supplementation), and food sources. (See sidebar for definition of terms, and see Appendix for a complete chart of vitamins.)

Water-Soluble Vitamins

Thiamin. Thiamin was the first vitamin to be identified. In modern times, thiamin deficiency is seen most commonly in association with chronic alcoholism. Only a small percentage of large doses are absorbed, and elevated serum levels result in its active urinary excretion. After an oral dose of the vitamin, peak excretion occurs in about two hours (Davis et al., 1984). Total body thiamin content in adults is approximately 30 milligrams with a half-life of 9 to 18 days (Ariaey-Nejad et al., 1970).

The recommended dietary allowance (RDA) for thiamin in adult women is 1.1 mg/day and in adult men it is 1.2 mg/day. The RDA for pregnancy and lactation is 1.4 mg/day (FNB, 1998). It should be noted that increased needs exist in persons being treated with hemodialysis or peritoneal dialysis, individuals with malabsorption syndrome, women carrying more than one fetus, and women nursing more than one infant.

There are no reports of adverse effects from the consumption of excess thiamin consumed in food or supplements. No upper level (UL) can be set due to the lack of reported findings associated with adverse effects. Supplements that contain up to 50 mg/day are available over-the-counter with no reported problems.

Food sources from which most of thiamin in the United States is derived include enriched, fortified, or whole-grain products, such as bread, bread products, mixed foods that contain grain, and ready-to-eat cereals. Foods that are especially rich in thiamin include yeast, lean pork, and legumes. Thiamin is absent from fats, oils, and refined sugars. Milk, milk products, seafood, fruits, and vegetables are not good sources.

Riboflavin. The second vitamin discovered was named vitamin B2 or riboflavin. Most dietary riboflavin is consumed as a complex of food protein. Signs of riboflavin deficiency are sore throat, redness, and edema of the throat and oral mucous membranes, cheilosis (cracking of the skin around the mouth), and glossitis (red tongue). Vitamin B2 deficiency most often occurs in combination with other nutrient deficiencies. The B vitamins are quite interrelated; for example, niacin requires riboflavin for its formation from the amino acid tryptophan, and vitamin B6 requires riboflavin for conversion to the active coenzyme form (McCormick, 1989).

The RDA for riboflavin has been set at 1.3 mg/day for men and 1.1 mg/day for women through age seventy years and older. For pregnancy, the RDA for riboflavin is set at 1.4 mg/day and it is 1.6 mg/day for lactation (FNB, 1998).

When riboflavin is absorbed in excess, very little is stored in the body tissues. Excess is excreted via the urine, and the amount varies with intake, metabolic events, and age (McCormick and Greene, 1994). No adverse effects associated with riboflavin consumption from food or supplements have been reported. No adverse effects were reported from a single dose of up to 60 milligrams and 11.6 milligrams of riboflavin given as a single intravenous (IV) dose (Zempleni et al., 1996).

The greatest contribution of riboflavin from the diet comes from milk and milk drinks, followed by bread products and fortified cereals. Especially good food sources of riboflavin are eggs, lean meats, milk, broccoli, and enriched breads and cereals. Recall that riboflavin loss occurs when it is exposed to light, so store milk in opaque containers or away from the light.

Niacin. The term "niacin" refers to nicotinamide and nicotinic acid. The coenzymes, the active form of niacin in the body, are synthesized in all tissues of the body. The amount of niacin in the body is the result of absorbed nicotinic acid and nicotinamide, as well as conversion of the amino acid tryptophan (60 milligrams of tryptophan = 1 milligram of niacin; Horwitt et al., 1981). Excess niacin is excreted through the urine.

Pellagra is the classical manifestation of niacin deficiency. Pellagra has been seen in areas where corn (low in niacin and tryptophan) is the dietary staple. Enrichment and fortification of grain has virtually eliminated pellagra from the United States and Europe.

The RDA for adult men is 16 mg/day of niacin equivalents, and the RDA for women aged nineteen to over seventy is 14 mg/day. In pregnant women the RDA is 18 mg/day of niacin equivalents and in lactating women it is 17 mg/day (FNB, 1998).

Niacin, given as nicotinic acid in doses from 4 to 6 g/day, is one of the oldest drugs used in the treatment of hyperlipidemia, which consists of elevated blood levels of triglycerides and cholesterol. Niacin lowers low-density lipoprotein (LDL) cholesterol and triglyceride concentration. This therapeutic effect is not seen with nicotinamide. Nicotinic acid in therapeutic doses can cause flushing and headache in some people. These side effects are not harmful.

An upper limit for niacin was set at 35 mg/day for adults, if the niacin is obtained from supplements, not foods. Individuals who take over-the-counter niacin to "self-medicate" may exceed the UL on a chronic basis. The UL is not intended to apply to those receiving niacin under medical supervision.

Vitamin B6. Vitamin B6 is a coenzyme for more than 100 enzymes involved in the metabolism of amino acids, glycogen, and nerve tissues (FNB, 1998). Microcytic anemia, reflecting decreased hemoglobin synthesis, can be seen in deficiency states. The interaction of vitamin B6 and folate (another B vitamin discussed below) has been shown to reduce the plasma concentrations of homocysteine and decrease the incidence of cardiovascular disease (CVD) risk (Rimm et al., 1998). Subjects with the highest intake of folate and vitamin B6 had a twofold reduction in CVD as compared to the group with the lowest intake.

In the 1970s there was quite a bit of discussion about the status of vitamin B6 in women using oral contraceptives. This was probably an artifact of hormonal stimulation of tryptophan catabolism rather than vitamin B6 deficiency. At the time these studies were conducted, estrogen concentrations were three to five times higher in contraceptive agents than they are today.

The RDA for vitamin B6 is 1.3 mg/day for adult men and women up to age fifty years. The RDA for people over fifty years of age is 1.7 mg/day for men and 1.5 mg/day for women. For pregnant women the RDA is set at 1.9 mg/day and for lactating women, 2.0 mg/day (FNB, 1998).

No adverse effects have been associated with intakes of vitamin B 6 from food. However, large doses of pyridoxine used to treat carpal tunnel syndrome and premenstrual syndrome have been associated with sensory neuropathy (Schaumburg and Berger, 1988). These findings were noted with dosages from 2 to 6 g/day. It appears that the risk of developing sensory neuropathy decreases quite rapidly at dosages below 1 g/day. Thus, the UL for adults is set at 100 mg/day of vitamin B6 as pyridoxine.

Food sources of vitamin B6 include fortified, ready-to-eat cereals; mixed foods with meat, fish, or poultry as the main ingredient: white potatoes, starchy vegetables, and noncitrus fruits. Vitamin B6 is widely distributed in foods; good sources are meats, whole-grain products, vegetables, and nuts.

Folate. Folate is a B vitamin that exists in many chemical forms (Wagner, 1996). Folic acid, the most stable form of folate, occurs rarely in food, but is the form used in supplements and fortified food products. Folate coenzymes are involved in numerous reactions that involve DNA synthesis, purine synthesis, and amino acid metabolism. The most well known is the conversion of homocysteine to methionine. It is this reaction that reduces the concentration of homocysteine in the plasma, and may lower the risk of cardiovascular disease (Rasmussen et al., 1996).

The metabolic interrelationship between folate and vitamin B12 may explain why a single deficiency of either vitamin leads to the same hematological changes. In either folate or vitamin B12 deficiency, megaloblastic changes occur in the bone marrow and other replicating cells.

Pregnant women are at risk for developing folate deficiency because of the heightened demands imposed by increased synthesis of DNA. Low folate status is associated with poor pregnancy outcome, low birth weight, and fetal growth retardation (Scholl and Johnson, 2000). Because of the possible incidence of neural tube defects (NTDs) during the preconception period (that is, just before
and during the first 28 days of conception), the Food and Nutrition Board recommends that women who are capable of becoming pregnant should consume 400 <g/day of synthetic folic acid, derived from dietary supplements or fortified food, in addition to their usual dietary intake (FNB, 1998). NTDs are the most common major congenital malformations of the central nervous system.

Recommendations for intake of folate are dependent on variation in bioavailability. Supplemental folate is nearly 100 percent absorbed, while absorption of folate found in foods is only about 50 percent. Fortified foods approach the level of bioavailability of folate found in supplements. This has led to the term Dietary Folate Equivalents or DFEs. Thus, dietary recommendations for folate intake are based on "folate equivalents." One <g of folate equivalents = 1 <g of food folate = 0.5 <g of folic acid taken on an empty stomach or = 0.6 <g folic acid with meals. The RDA for women is 320 <g dietary folate equivalents and for men it is 400 <g. During pregnancy 600 <g/day of folate is recommended and 500 <g/day is recommended during lactation (FNB, 1998).

No adverse effects have been associated with the consumption of normal folate-fortified foods. However, the risk of neurological effects that result from vitamin B12 deficiency that are masked with high doses of folate caused the FNB to set a UL. The UL for adults, nineteen years and older, is set at 1,000 <g/day of folate from fortified food or supplements.

Folates are found in nearly all natural foods. Protracted cooking or processing may destroy folate. Foods with the highest folate content include yeast, liver, other organ meats, fresh green vegetables, and some fruits (oranges, for example). Most of the dietary intake of folate in the United States comes from fortified ready-to-eat breakfast cereals followed by a variety of beans and peas, fresh and dried. As of 1 January 1998, all enriched cereal grains, pasta, flour, and rice are required to be fortified with folate at 1.4 mg/kg of grain.

Vitamin B12. Cyanocobalamin is the compound we call vitamin B12. This is the only vitamin B12 preparation used in supplements. An adequate supply of vitamin B12 is essential for normal blood formation and neurological function. The absorption of vitamin B12 is dependent on several physiological steps. In the stomach, food-bound vitamin B12 is dissociated from proteins in the presence of stomach acid. Vitamin B12 then binds with protein and in the intestine the vitamin B12 binds with intrinsic factor for absorption. If there is a lack of sufficient acid in the stomach or intrinsic factor in the intestine, malabsorption occurs and the resulting condition caused is pernicious anemia.

The anemia of vitamin B12 deficiency (completely reversed by addition of B12) is indistinguishable from that seen with folate deficiency. Because up to 30 percent of people older than fifty are estimated to have atrophic gastritis with low stomach acid secretion, older adults may have decreased absorption of B12 from foods. Thus, it is recommended that most of the vitamin B12 consumed by adults greater than fifty-one years of age be obtained from fortified foods or supplements.

The RDA of vitamin B12 for men and women is 2.4 <g/day, most of that amount coming from fortified foods or supplements in those over fifty years of age. During pregnancy, the RDA is 2.6 <g/day and it is 2.8 <g/day during lactation (FNB, 1998). No adverse effects have been associated with excess B12 intake from food or supplements. After reviewing the literature, the FNB found insufficient evidence for determining a UL.

Vitamin B12 is present in all forms of animal tissues. It is not present in plants and thus does not occur in fruits or vegetables. Because a generous intake of animal foods is customary in the United States, B12 intake from foods is usually adequate. People who avoid eating animal products may obtain most of their requirement through fortified foods.

Vitamin C. Ascorbic acid (the chemical name for vitamin C) is a potent antioxidant in animals and plants. Vitamin C is important in the synthesis of collagen. Some evidence indicates that vitamin C reduces virus activity by inhibiting viral replication (Johnston, 2001). Many anecdotal reports support a role for vitamin C supplementation to reduce the severity of cold symptoms.

Non-heme iron absorption from food is enhanced two-to threefold in the presence of 25 to 75 mg of vitamin C, presumably because of the ascorbate-induced reduction of ferric iron to ferrous iron, which is less likely to form insoluble complexes in the intestine. However, vitamin C has no effect on increasing iron absorption from heme iron (Johnston, 2001). Unlike most animal species, humans lack the ability to synthesize ascorbic acid; thus, the diet is the sole source for this vitamin.

The current requirement of vitamin C is 90 mg/day for adult men and 75 mg/day for adult women. During pregnancy the RDA is 85 mg/day, and 120 mg/day during lactation. The UL for vitamin C was set at 2 g/day (FNB, 2000). This level was set as a guideline for people using dietary supplements and was based on reports of gastrointestinal symptoms reported when too much vitamin C was taken.

Almost 90 percent of vitamin C in the diet comes from fruits and vegetables, with citrus fruits, tomatoes, tomato juice, and potatoes being the major contributors. It is also added to some processed foods as an antioxidant.

Pantothenic acid. Pantothenic acid was named after the Greek, meaning "from everywhere," because it is so
widespread in foods. Pantothenic acid is essential in the diet because of the inability of animals and humans to synthesize the pantoic acid moiety of the vitamin. Pantothenic acid plays a primary role in many metabolic processes, such as oxidative metabolism, cell membrane formation, cholesterol and bile salt production, energy storage, and activation of some hormones (Miller et al., 2001).

Pantothenic acid deficiency in humans is rare because of its ubiquitous distribution in foods. Many health claims are made regarding the role of pantothenic acid in ameliorating rheumatoid arthritis, lowering cholesterol, enhancing athletic performance, and preventing graying of hair (Miller et al., 2001). However, sufficient information is lacking at this time and so firm recommendations may not be made. No reports of adverse effects of oral pantothenic acid in humans have been reported.

The Food and Nutrition Board (1998) established an adequate intake level (AI) for pantothenic acid of 5.0 mg/day for adult men and women, 6.0 mg/day during pregnancy, and 7.0 mg/day during lactation. As mentioned above, pantothenic acid is found in a wide variety of both plant and animal foods. Because of its thermal lability and susceptibility to oxidation, significant amounts are lost during processing. Rich food sources include chicken, beef, liver, and other organ meats, whole grains, potatoes, and tomato products.

Biotin. In mammals, biotin serves as a coenzyme for reactions that control such important functions as fatty acid metabolism and gluconeogenesis. Biotin is recycled upon degradation of enzymes to which it is bound. Biotin from pharmaceutical sources is 100 percent bioavailable. Deficiency is rare but has been seen in patients on parenteral nutrition without biotin supplementation (Zempleni and Mock, 1999). Lipoic acid and biotin have structural similarities, thus competition potentially exists for intestinal or cellular uptake. This may be of concern in settings where large doses of lipoic acid are administered or taken as supplements (Zempleni et al., 1997).

The Food and Nutrition Board established an AI for biotin due to insufficient data to set an RDA. Adult men and women have an AI of 30 <g/day (FNB, 1998). It is the same for pregnancy and increases to 35 <g/day during lactation. No adverse effects of biotin have been reported. Toxicity has not been reported in patients receiving up to 200 mg orally daily or up to 20 mg intravenously.

Biotin is distributed widely in natural foods. Those rich in biotin include egg yolk, liver, and some vegetables. It is estimated that individuals in the United States consume between 35 and 70 <g/day.

Choline. Choline has been considered a nonessential nutrient because humans can synthesize sufficient quantities. However, when hepatic function is compromised, hepatic choline synthesis is decreased and thus choline is now considered "conditionally" essential. In a 1998 report from the Food and Nutrition Board, choline is considered an essential nutrient (FNB, 1998). The Food and Nutrition Board noted that additional studies on the essentiality for human nutrition are needed. Specifically, the 1998 Food and Nutrition Board study suggested that graded doses of choline intake be studied regarding their effects on organ function, plasma cholesterol, and homocysteine levels.

Choline functions as a precursor for phospholipids and acetylcholine, and betaine. The AI for adult men was set at 550 mg/day and for women at 425 mg/day. For pregnancy, the AI was increased to 450 mg/day and during lactation, to 550 mg/day (FNB, 1998). Due to reports of hypotension (low blood pressure) from excess intake, a UL was set at 3.5 g/day for persons nineteen years and older. Choline and choline-containing lipids, mainly phosphatidylcholine, are abundant in foods of both plant and animal origin. Rich sources include muscle and organ meats and eggs. To date there are no nationally representative estimates of choline intake from food or supplements.

Fat-Soluble Vitamins

Vitamin A. The active forms of vitamin A participate in three essential functions: visual perception, cellular differentiation, and immune function. A number of food sources are available for vitamin A. Preformed vitamin A is abundant in animal foods and provitamin A carotenoids are abundant in dark-colored fruits and vegetables. With a 2001 report from the Food and Nutrition Board (FNB 2001), there has been recognition of a change in equivalency values of various carotenoids to vitamin A. Retinol activity equivalents (RAEs) for dietary provitamin A carotenoids—beta-carotene, alpha-carotene, and betacryptoxanthin—have been set at 12, 24, and 24 <g, respectively (see Table 1, below). This decision is based on an extensive review of studies, which are summarized in the FNB report (2001) (see Table 1).

A number of factors affect the bioavailability of carotenoids (Castenmiller and West, 1998). Percent absorption

Dietary forms of vitamin A and provitamin A carotenoids

Consumed

Absorbed

Bioconverted

Dietary or supplemental Vitamin A (1 μg)

Retinol

Retinol (1 μg)

Supplemental beta-carotene (2 μg)

beta-carotene

Retinol (1 μg)

Dietary beta-carotene (12 μg)

beta-carotene

Retinol (1 μg)

Dietary alpha-carotene or beta-cryptoxanthin (24 μg)

alpha-carotene or beta-cryptoxanthin

Retinol (1 μg)

SOURCE: Adapted from FNB 2001

decreases as the amount of dietary carotenoids increases, and the relative carotene concentration absorbed increases when consumed with oil or associated with plant matrix material. That is part of the plant vitamin source, not separated out as a supplement. The presence of dietary fat stimulates the secretion of bile acids and improves the absorption of carotenoids.

Recommended dietary allowance for men is 900 <g/day of vitamin A and for women 700 <g/day. During pregnancy, RDA is set at 770 <g/day and 1,300 <g/day during lactation. Human infants consume about 400 <g/day of vitamin A in the first six months of life (FNB, 2001).

Based on the literature review, the FNB used liver abnormalities as the critical adverse effect for setting the UL for adults. Issues of carcinogenicity were considered for women of childbearing age. The UL varies slightly with age between 2,800 and 3,000 <g/day of preformed vitamin A in food or supplements for adolescents and adults. Note that alcohol intake enhances the toxicity of vitamin A.

The richest sources of vitamin A are fish oils, liver, and other organ meats. Whole milk, butter, and fortified margarine and low-fat milks are also rich in the vitamin. In the United States carrots, fortified spreads, and dairy products are the leading contributors of vitamin A to the diet.

Vitamin D. Vitamin D is essential for life in higher animals. It is one of the most important regulators of calcium homeostasis and was historically considered the "anitrachitic" factor. The biological effects of vitamin D are achieved only by its hormonal metabolites, including two key kidney-produced metabolites: 1,25(OH)2 vitamin D and 24,25(OH) vitamin D. In addition to its role in calcium metabolism, research has identified that vitamin D plays an important role in cell differentiation and growth of keratinocytes and cancer cells and has shown that it participates in the process of parathyroid hormone and insulin secretion (Bouillon et al. 1995).

Vitamin D3, the naturally occurring form of the vitamin, is produced from the provitamin, 7-dehydrocholesterol, found in the skin under the stimulation of ultraviolet (UV) irradiation or UV light. Vitamin D2 is a synthetic form of vitamin D that is produced by irradiation of the plant steroid ergosterol. A requirement for vitamin D has never been precisely defined because vitamin D is produced in the skin after exposure to sunlight. Therefore, humans do not have a requirement for vitamin D when sufficient sunlight is available. The fact that humans wear clothes, live in cities where tall buildings block the sunlight, use synthetic sunscreens that block UV rays, and live in geographical regions of the world that do not receive adequate sunlight contributes to the inability of the skin to synthesize sufficient vitamin D (Holick, 1995). Exposure to the sun sufficient for humans to obtain enough UV radiation to synthesize adequate vitamin D can be as little as three weekly exposures of the face and hands to ambient sunlight for 20 minutes (Adams et al., 1982).

A substantial proportion of the U.S. population is exposed to suboptimal levels of sunlight during the winter months. Under these conditions, vitamin D becomes a true vitamin and must be supplied regularly in the diet. The Food and Nutrition Board recommend an AI or adequate intake of vitamin D at 200 IU/day (5 <g) for adults up to fifty years of age (FNB, 1997). For adults over fiftyone, the AI is set at 400 IU/day (10 <g).

To prevent life-threatening hypercalcemia, an upper level (UL) for vitamin D has been set at 2,000 IU/day (50 <g) for adults over age eighteen. The use of 1,25 (OH)2 vitamin D for treatment of hypoparathyroidism, vitamin D–resistant rickets, renal osteodystrophy, osteoporosis, and psoriasis opens the door for potential toxicity because this form of the vitamin is much more toxic and the body's metabolic controls are bypassed. When this medication is being used, careful monitoring of plasma calcium concentrations is required.

Salt-water fish are good unfortified sources of vitamin D. Small quantities are derived from eggs, beef, butter, and vegetable oils. Fortification of milk, butter, margarine, cereals, and chocolate mixes help in meeting the dietary requirements. Excessive amounts of vitamin D are not available in usual dietary sources. However, excessive amounts can be obtained through supplements that result in high plasma levels of 25(OH) vitamin D.

Vitamin E. Vitamin E (also called tocopherol) is found in cell membranes and fat depots. Because of their chemical structure, there are eight stereoisomers of each of the tocopherols. In addition to each of the stereoisomers, each occur in alpha, beta, gamma, and delta forms (FNB, 2000).

Its most recognized function is to protect polyunsaturated fatty acids (PUFA) from oxidation. PUFAs are particularly sensitive to oxidative damage, and the protective role of vitamin E is supported by a similar antioxidant protection from vitamin C and selenium. One tocopherol molecule can protect 100 or more PUFA molecules from autoxidative damage (Pryor, 2001).

The various forms of vitamin E have different biological activity, with the natural source isomer—R,R,R,-alpha-tocopherol—being the most active. In supplements you may see this isomer called by its former name, d -alpha-tocopherol. Synthetic vitamin E is called all -rac -alpha-tocopherol or dl -alpha-tocopherol in supplements. Biological activities of vitamin E are given in the older international units (IU) or alpha-tocopherol equivalents (alpha-TE). Because of the many forms of vitamin E in plants and available synthetically, the relative activities of each form is complex. Current evidence indicates that vitamin E from natural sources has approximately twice the bioactivity in humans that the all-rac (synthetic) vitamin does (Burton et al., 1998).

Based on the literature review, FNB used hemorrhagic (bleeding) effects for the criteria to set the UL. For adults nineteen years and older the UL is 1,000 mg (2,326 mol)/day of any form of supplementary alpha-tocopherol. There is no evidence of adverse effects from intake of vitamin E naturally occurring in foods.

The RDA for vitamin E is 15 mg/day of naturally occurring alpha-tocopherol for adults above nineteen years of age (FNB, 2000). During pregnancy 15 mg/day is recommended and 19 mg/day for lactation.

The tocopherol content of foods varies widely depending on storage, processing, and preparation. The best sources of vitamin E are the common vegetable oils and products made from them. However, most of the tocopherols may be removed in processing. Wheat germ and walnuts also have high amounts of tocopherols.

Vitamin K. Vitamin K was named after the first letter of the German word Koagulation. For many years blood coagulation was assumed to be the sole physiological role for vitamin K. We now know that vitamin K plays an essential role in the synthesis of proteins including prothrombin and the bone-forming protein, osteocalcin (Vermeer et. al., 1995).

Dietary vitamin K absorption is enhanced by dietary fat and is dependent on bile and pancreatic enzymes. The human gut contains large amount of bacterially produced vitamin K, but its contribution to the maintenance of vitamin K status has been difficult to assess (Suttie, 1995). The vitamin K produced by bacteria in the gut is less biologically active even though it is stored in the liver and present in blood. Current understanding supports the view that this vitamin K source may partially satisfy the human requirement but that the contribution is much less than previously thought.

The drug warfarin, widely prescribed as an anticoagulant, functions through inhibition of vitamin K. As a result, alterations in vitamin K intake can influence the efficacy of warfarin. The effective dose of warfarin varies from individual to individual, as does the dietary intake of vitamin K. The best solution appears to be to establish the necessary dose of warfarin and urge patients to maintain a constant intake of foods high in vitamin K in their diets. Only a small number of food items contribute substantially to the dietary vitamin K.

The recommended intake is based on an AI or adequate intake of 120 <g/day for men, 90 <g/day for women, and 90 <g/day during pregnancy and lactation (FNB, 2001). No adverse effects have been associated with vitamin K intake in humans from food or supplements. Thus, no UL is set for vitamin K.

Collards, spinach, and salad greens are high in vitamin K. Broccoli, Brussels sprouts, cabbage, and Bib lettuce contain about two-thirds as much, and other green vegetables contain even less. Vitamin K is also found in plant oils and margarine, with soybean and canola oils having the highest amounts. U.S. food intake surveys indicate that spinach, collards, broccoli, and iceberg lettuce are the major contributors of vitamin K in the diet.

Dietary Reference Intakes

See Appendix for full chart of Dietary Reference Intakes.

Recommended Dietary Allowance (RDA)—the dietary intake level that is sufficient to meet the nutrient requirement of nearly all (97 to 98 percent) healthy individuals in a particular life stage and gender group.

Adequate Intake (AI)—a recommended intake value based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of healthy people that are assumed to be adequate—used when an RDA cannot be determined.

Tolerable Upper Intake Level (UL)—the highest level of nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the general population. As intake increases above the UL, the risk of adverse effects increases.

Vitamins

Science of Everyday Things
COPYRIGHT 2002 The Gale Group Inc.

VITAMINS

CONCEPT

Most of us have been told to take our vitamins, but few people know why, and despite all the talk about them in modern culture, vitamins remain something of a mystery. Vitamins are organic substances, essential for maintaining life functions and preventing disease among humans and animals and even some plants. They are found in very small quantities in food; certain health specialists recommend taking vitamin supplements to augment the supplies in food, while others insist that a well-balanced diet provides all the vitamins that an ordinary person needs. Some vitamins, such as vitamin C and the B complex, are water-soluble, which means that they are excreted easily and must be ingested every day. Others, such as vitamins A, D, E, and K, are fat-soluble and therefore are retained in the body's fatty tissues. With such vitamins, there may be a danger of taking too much, but in the case of most vitamins, the greatest harm comes from not receiving enough. Vitamin deficiencies can be the cause of rickets, pellagra, and other diseases that have plagued the poor in the Western world and the third world in the past and in the present.

HOW IT WORKS

An Introduction to Vitamins

Once they were called vitamines, but for reasons that we address later, the "e" was dropped, and they became known as vitamins. There is also a reason for the strange alphabet of vitamins (A, B, C, D, E, K), which, like the change in spelling, came out of the early days of scientific research into the subject during the first third of the twentieth century. Though people did not know about vitamins per se until that time, folk wisdom certainly had taken account of the fact that certain foods are essential to the health and well-being of humans and animals.

Vitamins may be defined as organic substances, found in food, that are essential in very small quantities for the health of most animals and some plants. Organic substances, discussed in The Biosphere, are compounds (substances in which atoms of more than one element are chemically bonded to one another) containing hydrogen and carbon. Primarily, vitamins work with enzymes (protein materials that speed up chemical reactions in the bodies of plants and animals) in regulating metabolic processes—that is, processes that convert food to energy. They do not in themselves provide energy, however, and thus vitamins alone do not qualify as a form of nutrition.

Organisms require vitamins only in very small amounts: the total amount of vitamin mass a person needs in one day, for instance, is only about 0.0011 lb. (0.5 g). Yet vitamins are absolutely essential to the maintenance of health and for disease prevention, and most animals are not capable of synthesizing or manufacturing vitamins on their own. Nonetheless, most animals can produce vitamin C, though there are exceptions—humans included.

Animals depend on plants for their nutrition, either directly or indirectly (i.e., either by consuming the plant or by consuming an animal that has consumed the plant). Plants, on the other hand, are autotrophs, meaning that they can meet their nutritional needs with only sunlight, water, and a few chemical compounds. Among the nutrients plants produce are vitamins,
which they pass on to animals that consume them directly or indirectly. (See Food Webs for more about autotrophs and the relationship of animal consumers to them.)

Classifying Vitamins

Numerous vitamin groups are necessary for the nutritional needs of humans, and though only minute amounts of each are required to achieve their purpose, without them life could not be maintained. Some vitamins, including A, D, E, and K, are fat-soluble, meaning that they are found in fattier foods and in body fat. Thus, they can be stored in the body; for this reason, it is not necessary to include them in the diet every day. In fact, it could be dangerous to do so, since it is possible that they would build up to toxic levels in the tissues. Other vitamins, the most notable of which are vitamin C and the many vitamins in what is known as the "B complex," are water-soluble. They are found in the watery parts of food and body tissue, and because they are excreted regularly in the urine, they cannot be stored by the body. Instead, they must be consumed on a daily basis. This difference in solubility is extremely important to the way the vitamins function within an organism and in the ways and amounts in which they are consumed.

THE NAMES OF VITAMINS.

Vitamins originally were classified in terms of their solubility in water or in fat, and these distinctions remain important for the reasons outlined above. Today, vitamins are known primarily by letters of the alphabet, a fact that harks back to a naming system developed as more and more vitamins were discovered in the early years of the twentieth century.

As scientists detected the existence of more vitamins, or what they thought were vitamins, they assigned to them successive letters of the alphabet: A, B, C, and so on. Eventually, however, they discovered that some substances originally thought to be vitamins were not vitamins, and they removed them from the roster. For example, what used to be called vitamin F is simply an essential fatty acid, a necessary component of the diet of a mammal but not the same thing as a vitamin. In other cases, what were once believed to be individual vitamins later were subsumed into the B complex. Among these substances are riboflavin, formerly termed vitamin G, and biotin, once called vitamin H. The result is that today the only alphabetical vitamin names are A, the B complex, C, D, E, and K.

REAL-LIFE APPLICATIONS

Fat-Soluble Vitamins

We are accustomed in modern life to being told that fat is bad for us, but to quote a much-cited line from the American composer George Gershwin's opera Porgy and Bess, "It ain't necessarily so." Fat is not inherently bad for people; in fact, a certain amount in the diet is essential. The problem in America today is the type of fat that people consume. There is a big difference between the healthy, natural, unsaturated fats one might find, say, in fresh salmon, and the highly processed and saturated fats in a bag of potato chips. (The term saturated means that every gap in which a hydrogen atom could fit in a string of carbon and hydrogen atoms has been filled. This helps make fats firm, for use in such products as shortening.)

Such fat is extremely harmful, because the body is not able to process it; even so, a certain amount of natural fat in the diet can be highly beneficial. This is true in large part because fat can serve as a medium for the fat-soluble vitamins A, D, E, and K, which are deposited in the body's fat cells. But as we noted earlier, it is important not to overdose on fat-soluble vitamins, because then what is inherently healthy can become extremely unhealthy.

VITAMIN A.

In 1596 the Dutch explorer Willem Barents (1550-1597) and his shipwrecked crew spent a grueling winter on the island of Novaya Zemlya in the Arctic Ocean north of Russia. They had sailed from Holland in search of the Northeast Passage, which, like the more famous Northwest Passage above Canada, offered the prospect of a short, relatively direct sea route from Europe to Asia and the Americas. The problem was that the ice made sailing the northern seas virtually impossible. It would be almost three centuries before a crew managed to negotiate the Northeast Passage, by which time the European powers had long since given up all hopes of using it as a viable sailing route. (The same was true of the Northwest Passage, which was not traversed until 1906.)

Barents and his men knew none of that, nor would they have cared in that miserable winter of 1596-1597. All they cared about was survival, the chances for which seemed slim—and not just because of the almost inhuman cold or the fact that their ship had been cracked to pieces by the ice. Men were dying of scurvy, a vitamin-deficiency disease we discuss later in the context of vitamin C, as well as from the cold. Yet there were a few blessings, mainly in the form of available wood for fuel and animals for food. The men killed polar bears and ate their meat, and no doubt they were thankful just to stay alive. They could not have guessed, however, that they were actually killing themselves with an overdose of vitamin A.

Just 1 lb. (0.454 kg) of polar bear liver contains about 450 times the recommended daily dose of vitamin A, and the men in Barents's expedition were absorbing far more of the vitamin than they should have. In time, they began to experience the effects of vitamin A poisoning: painful joints, bone thickening, peeling of the skin over the entire body, and chronic liver disease. When spring came, the men managed to make it off the island, but many of them—Barents included—never lived to see Holland again, in part because the side effects of vitamin A toxicity had weakened them.

So why take vitamin A at all? Because it is necessary for proper growth of bones and teeth, for the maintenance and functioning of skin and mucous membranes, and for the ability to see in dim light. There is some evidence that it can help prevent cataracts (a clouding of the lens in the eye) and cardiovascular disease, a condition of the heart and circulatory system. Furthermore, when taken at the onset of a cold, vitamin A can ward off the illness and fight its symptoms.

One of the first signs of vitamin A deficiency is "night blindness," in which the rods of the eye (necessary for night vision) fail to function normally. Extreme cases of vitamin A deficiency can lead to total blindness. Other symptoms include dry and scaly skin, problems with the mucous linings of the digestive tract and urinary system, and abnormal growth of teeth and bones. The bodies of healthy adults who have an adequate diet can store several years' supply of this vitamin, but young children, who have not had time to build up such a large reserve, suffer from
deprivation much more quickly if they do not consume enough.

Vitamin A is present in meats (mainly liver), fish oil, egg yolks, butter, and cheese. Although plants do not have vitamin A, dark green leafy vegetables and yellow fruits and vegetables (e.g., carrots, sweet potatoes, cantaloupe, corn, and peaches) contain a substance called beta-carotene, which is converted to vitamin A in the intestine and then absorbed by the body. It is nearly impossible to ingest beta-carotene in toxic amounts, unlike vitamin A from animal sources, since the body will not convert excess amounts to toxic levels of vitamin A.

VITAMIN D.

Vitamin D is actually two different substances, D2 and D3. (There was no D1, since the substance designated thus at one time turned out to be a mixture of several compounds, including calciferol, or D2) Both forms of vitamin D are activated, or made effective, by
sunlight, and for this reason vitamin D often is called the sunshine vitamin. It is hard to suffer a vitamin D deficiency if one gets enough sunshine in combination with consuming such foods as eggs (specifically, the yolk), such fatty fish as salmon, and enriched milk. (Milk does not naturally contain vitamin D, but the vitamin is sometimes included as an additive.)

Vitamin D lets the body utilize calcium and phosphorus in bone and tooth formation, and a deficiency causes a bone disease called rickets. Under the influence of this physically debilitating and disfiguring disease, legs become bowed by the weight of the body, and the wrists and ankles thicken. The teeth are badly affected and, for a young child, take much longer to mature. Infants and children are most likely to suffer the effects of rickets, but since all milk and infant formulas have vitamin D added to them, the condition is seen rarely in the industrialized world today. In the brutal early days of the Industrial Revolution, however (i.e., in Englandca. 1760-1830), crowded slum conditions in areas where there was little or no sunlight made possible many cases of rickets.

Whereas rickets primarily affects children, adults may suffer from a disease called osteomalacia, caused by a deficiency of vitamin D, calcium, and phosphorous. Sometimes seen in the Middle East and other parts of Asia, osteomalacia brings with it rheumatic pain and causes the bones to become soft and deformed. As with rickets, the treatment for osteomalacia is a combination of calcium, phosphorous, and vitamin D. On the other hand, as with all fat-soluble vitamins, a person may take in excessive amounts of vitamin D, which has its own ill effects: nausea, diarrhea, weight loss, and pain in the bones and joints. Damage to the kidneys and blood vessels also can occur as calcium deposits build up in these tissues.

VITAMIN E.

Composed of at least seven similar chemicals called the tocopherols, vitamin E is found in green leafy vegetables, wheat germ and other plant oils, egg yolks, and meat. The main function of this vitamin is to act as an antioxidant, to counteract the harmful effects oxygen can have on tissues. It may seem strange to speak of oxygen causing harm, since it is essential to life, but oxidation is an extremely powerful chemical reaction that, under various conditions, can manifest as rotting or putrefaction, rusting, or even combustion and explosion. When an apple turns brown a few minutes after you have cut it open, it is the result of oxidation.

Oxidation also may be linked to the effects of aging in humans as well as to other conditions, such as cancer, hardening of the arteries, and rheumatoid arthritis. It appears that oxygen molecules, which draw electrons to them, extract these electrons from the membranes in human cells. Over time, this can cause a gradual breakdown in the body's immune system. Antioxidants, such as vitamin E or beta carotene, therefore may be important in preserving human health and well-being.

Vitamin E is particularly important for counteracting oxidation in fats. When they are oxidized, fats form a highly reactive substance called peroxide, which is often very damaging to cells. Vitamin E is more reactive (i.e., more likely to form or break chemical bonds) than the fatty acid molecule, and, therefore, the vitamin reacts instead of the fat. Because cell membranes are composed partly of fat molecules, vitamin E is vitally important in maintaining the nervous, circulatory, and reproductive systems and in protecting the kidneys, lungs, and liver.

Because vitamin E is so common in foods, it is very difficult to suffer from a deficiency of this vitamin unless a person avoids consuming fats altogether—another example of why a no-fat diet is not a healthy one. The effects of vitamin E deficiency, all of which are apparently linked to the loss of its antioxidant protection, include cramping in the legs, fibrocystic breast disease (a condition that involves the formation of lumps and cysts in the breasts), and even muscular dystrophy. The seriousness of the latter two diseases only serves to highlight the importance of vitamin E to the body.

VITAMIN K.

Like vitamin D, vitamin K is composed of two groups of compounds, vitamins K1 and K2. There is also a substance called K3, but this vitamin is actually menadione, a synthetic compound from which the other forms of K are derived. You can find vitamin K in many plants, especially green leafy ones such as spinach, and in liver. Vitamin K is also made by the bacteria that live in the intestine—the "good" bacteria that help make possible the processing of food through the body.

Vitamin K appears to be critical to blood clotting, thanks to its role in assisting the formation of a chemical called prothrombin in the liver.
Deficiencies of this vitamin rarely occur as the result of an incomplete diet; instead, it is usually a consequence of liver damage and the blood's inability to process the vitamin. The deficiency manifests in unusual bleeding or large bruises under the skin or in the muscles. Adults in the West seldom experience vitamin K deficiencies, but newborn infants have been known to suffer from brain hemorrhage owing to a lack of this vitamin.

Water-Soluble Vitamins

B VITAMINS.

The two water-soluble vitamins, as we shall see, have played a major part in medical history. Actually, there are more than two water-soluble vitamins, because vitamin B is really a complex of about a dozen vitamins—hence, the name B complex. Among them are vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B6 (pyridoxine), and vitamin B12 (cobalamin). A few others—for example, niacin (vitamin B7) and pantothenic acid (vitamin B3), are known better by names other than their "B names," while biotin and folate, or folic acid, are not known by "B names" at all.

Vitamin B1, present in whole grains, nuts, legumes (e.g., peas), pork, and liver, helps the body release energy from carbohydrates. More than 4,000 years ago, the Chinese described a disease we know today as beriberi, which affects the nervous and gastrointestinal systems and causes nausea, fatigue, and mental confusion. The cause of beriberi is a deficiency of thiamine, or B1, found in the husks or bran of rice and grains. White rice, which most people find more pleasing to the palate than brown rice, is the result of a milling and polishing process in which the husks—and along with them, this important nutrient—are removed. Manufacturers today produce "enriched" rice, flour, and other grain products by adding thiamine back in, but until scientists discovered the importance of thiamin in grain husks, many people, especially in the Far East, suffered the effects of beriberi. (Early research on beriberi will be discussed later.)

Vitamin B2 helps the body release energy from fats, proteins, and carbohydrates. It can be obtained from whole grains, organ meats (e.g., liver), and green leafy vegetables. Lack of this vitamin causes severe skin problems. Vitamin B6 is important in the building of body tissue as well as in protein metabolism and the synthesis of hemoglobin (an iron-containing pigment in red blood cells that is responsible for transporting oxygen to the tissues and removing carbon dioxide). A deficiency can cause depression, nausea, and vomiting. Vitamin B12 is necessary for the proper functioning of the nervous system and in the formation of red blood cells. It can be obtained from meat, fish, and dairy products. Anemia (a lack of red blood cells, which produces a lethargic condition), nervousness, fatigue, and even brain degeneration, can result from vitamin B12 deficiency.

Niacin is also highly important to human health, as we explain later in the context of the disease pellagra. Pantothenic acid helps release energy from fats and carbohydrates and is found in large quantities in egg yolks, liver, eggs, nuts, and whole grains. Deficiency of this vitamin causes anemia. Biotin, widely available from grains, legumes, and liver, plays a part in the release of energy from carbohydrates and in the formation of fatty acids. A lack of biotin causes dermatitis, or skin inflammation.

VITAMIN C.

The American chemist and peace activist Linus Pauling (1901-1994), winner of the Nobel Prize in chemistry (1954) and peace
(1962), helped popularize vitamin C, also known as ascorbic acid. It was Pauling who originated the idea, now widespread in society, that massive doses of vitamin C can ward off the common cold. Pauling went further, by maintaining that vitamin C offers protection against some forms of cancer. While scientific studies have been unable to prove this theory, they do suggest that the vitamin can at least reduce the severity of the symptoms associated with colds.

Most animals can synthesize this vitamin in the liver, where glucose (a type of sugar that occurs widely in nature) is converted to ascorbic acid. This is not the case with at least four types of animal: monkeys, guinea pigs, Indian fruit bats, and humans, all of which must obtain vitamin C from their diets. Citrus fruits, berries, and some vegetables (e.g., tomatoes and peppers) are good sources of vitamin C. It is a fragile vitamin, one that is oxidized or destroyed easily. Food storage or food processing can render it ineffective; so, too, can soaking vitamin C-containing fruits and vegetables in water for long periods.

Vitamin Deficiencies and History

Most of the early history in the study of vitamins centered around what are now known as the water-soluble vitamins. Although vitamins as such were not discovered until early in the twentieth century, it was common knowledge long before that time that substances in certain foods were necessary for good health. An important turning point came in the mid-eighteenth century, with the work of the Scottish physician James Lind (1716-1794) on a vitamin deficiency condition that jeopardized England's vast merchant and military navies.

At a time when England had emerged as the world's leading sea power, even Her Majesty's sailing crews were at the mercy of a condition known as scurvy. Common among crews who had been at sea too long, scurvy could result in swollen joints, bleeding gums, loose teeth, and an inability to recover from wounds. Scientists today recognize scurvy as resulting from a deficiency of vitamin C, available in such citrus fruits as oranges. At the time, however, the concept of vitamins was unknown, and sailors at sea continued to live on a diet that consisted primarily of salted meats and hard biscuits—items that could be stored easily without spoilage in an era before refrigeration.

In 1746, Lind, a ship's doctor, observed that 80 of 350 seamen aboard his ship came down with scurvy during a 10-week cruise. Conducting a controlled experiment, he took 12 of the sailors in whom scurvy had developed and divided them into six groups. He gave each pair different substances, such as nutmeg, cider, seawater, and vinegar; the final pair was given lemons or oranges. The two men given the oranges and lemons both completely recovered in about a week. Not only was this a milestone in the history of vitamin research, but it also was the first example of a clinical trial, or the testing of a medication by careful and well-documented experimentation in which other variables or factors are kept unchanged.

It would be another half-century before the British navy adopted Lind's techniques. Another Scottish physician, Sir Gilbert Blane (1749-1834), had long fought for the adoption of Lind's methods, and finally, in 1796, he persuaded the navy to give each sailor a daily ration of lemons. At that time, the term lime was common for both lemons and limes, and, as a result, British sailors became known as limeys. Eventually, the treatment spread to the population as a whole, but outbreaks of scurvy continued until after World War I, when doctors isolated vitamin C as the controlling factor in scurvy prevention.

BERIBERI IN THE DUTCH EAST INDIES.

In 1897 the Dutch government sent the physician Christiaan Eijkman (1858-1930) as part of a government commission to the Dutch East Indies (now Indonesia), which had been long afflicted by a condition known as beriberi. There are various forms of this disease, including infant beriberi, which can kill a breast-feeding baby after the fifth month, as well as various juvenile and adult forms. In the childhood and adult versions of the disease, there is a preliminary condition of fatigue, loss of appetite, and a numb, tingling feeling in the legs. This condition can lead to either wet beriberi, characterized by the accumulation of fluid throughout the body and a rapid heart rate that can bring about sudden death, or dry beriberi,
which is marked by a loss of sensation and weakness in the legs. The patient first needs to walk with the aid of a stick and then becomes bedridden and easy prey to infectious diseases.

Experimenting with birds, Eijkman noticed that some of the fowl experienced paralysis and polyneuritis (a disorder affecting several nerves at once), as in the dry form of beriberi. The director
of the hospital had told Eijkman that he could not feed the birds with table scraps from the dining hall, where the diet was heavy in polished rice. The doctor thus was forced to feed his birds whole rice, and something amazing happened: the birds began to regain their ability to move and experienced no recurrence of paralysis.

Eijkman's colleagues rejected his claim that the birds had contracted some form of beriberi, though, in fact, he was correct. He was incorrect, however, in his supposition that the polished rice contained a toxin that was missing from the whole, unpolished rice. After Eijkman and the rest of the medical commission left the East Indies, another Dutch physician, Gerrit Grijns (1865-1944), stayed on to study the disease. He discovered that when the chickens were taken off the rice diet completely and fed meat instead, they did not show signs of the characteristic paralysis; if the meat was overcooked, however, the condition reappeared. In 1901, Grijns showed that beriberi could be cured by putting the rice polishings back into the rice. As it turned out, the husks and the meat contained vitamin B1, also present in wheat germ, whole grain and enriched bread, legumes, peanuts, and nuts.

PELLAGRA IN THE AMERICAS.

A vitamin-deficiency disease often associated with poverty, pellagra produces symptoms known as the "three Ds": diarrhea, dermatitis, and dementia, or mental deterioration. It was first identified in 1762 by the Spanish physician Gaspar Casal (ca. 1680-1759), who wrote about the "mal de la rosa"—so called because of the reddened dermatitis that appeared around the back of the victim's neck—that afflicted sufferers in one particular region of Spain.

Casal was far ahead of his time in maintaining that inadequate nutrition caused pellagra, but for many centuries the belief persisted that the disease resulted from infection. The breakthrough came with the work of the American physician Joseph Goldberger (1874-1929), a member of the U.S. Public Health Service who studied the high numbers of pellagra cases among poor blacks and whites in the southern United States. Goldberger established that pellagra stems from insufficient niacin, which is required to release energy from glucose.

Niacin is present in whole grains, meat, fish, and dairy products. One of the foods from which niacin is not easily available is corn, and it so happened that corn products constituted a major part of the diet in areas suffering from high rates of pellagra. The poor of Spain and Latin America subsisted on a diet heavy in corn products, such as tortillas and polenta, while their counterparts in the southern United States survived on cornbread, grits, hominy, and other variants of corn. Although such foods made it possible to fill the stomach cheaply, this diet was killing people in large numbers because it was not delivering the essential B vitamin niacin.

MODERN KNOWLEDGE OF VITAMINS.

As it turned out, corn, in fact, does contain niacin, but to release the niacin from the large, fibrous molecules in corn, it is necessary to treat the corn with an alkaline solution, such as limewater. This is just one example of the vast knowledge that has accumulated since the time when the Polish-American biochemist Casimir Funk (1884-1967) coined the term vitamine in 1912. The first half of the word came from the Latin vita, or "life," and the second half reflected Funk's belief that all these substances belonged to a group of chemicals known as amines. Scientists later dropped the "e" when they discovered that not all vitamins contain an amine group.

In the director Stephen Spielberg's acclaimed 1987 film Empire of the Sun, one of the characters asks another, "Do you believe in vitamins?" The question reflects the relative newness of vitamins as an idea at the time when the movie was set, during World War II. After the war, interest in commercially produced vitamin supplements exploded, particularly among America's middle classes. Pauling's promotion of vitamin C, coming in the 1950s and 1960s, found a willing audience.

Although vitamin supplements remain a big business today, opinions vary as to the importance of enhancing one's diet with them. Many nutritionists insist that eating a well-balanced diet, consisting of the major food substances, is an effective and economical way to obtain nutrients for health. On the other hand, advocates of health foods and alternative medicine (medical practices that are not recognized officially by groups of university-trained and state-licensed medical doctors) insist that the recommended daily allowances established by the U.S. Food and Drug Administration do not provide sufficient vitamins for an average person.

The American Dietetic Association (ADA) recommends that nutrient needs come from a variety of foods taken from different dietary sources rather than from self-prescribed vitamin supplements. The organization makes allowances, however, for supplement usage by people who need extra doses of key vitamins and minerals. Examples include the use of iron supplements by women experiencing heavy menstrual bleeding as well as supplements of iron, folic acid, and calcium by pregnant women.

KEY TERMS

AMINO ACIDS:

Organic compounds made of carbon, hydrogen, oxygen, nitrogen, and (in some cases) sulfur bonded in characteristic formations. Strings of amino acids make up proteins.

ANEMIA:

A condition marked by a lack of red blood cells or hemoglobin or a shortage in total blood volume, any one of which can produce a lethargic condition.

ANTIOXIDANT:

An enzyme, or some other organic substance, that is capable of counteracting the negative impact of oxygen (which draws electrons to it) on living tissue.

CARBOHYDRATES:

Naturally occurring compounds, consisting of carbon, hydrogen, and oxygen, whose primary function in the body is to supply energy. Included in the carbohydrate group aresugars, starches, cellulose, and various other substances.

COMPOUND:

A substance in which atoms of more than one element are bonded chemically to one another.

ENZYME:

A protein material that speeds up chemical reactions in the bodies of plants and animals.

GLUCOSE:

A type of sugar that occurs widely in nature. Glucose is the form in which animals usually receive carbohydrates.

HEMOGLOBIN:

An iron-containing pigment in red blood cells that is responsible for transporting oxygen to the tissues and removing carbon dioxide.

METABOLISM:

The chemical process by which nutrients are broken down and converted into energy or used in the construction of new tissue or other material in the body.

MINERALS:

Inorganic substances that, in a nutritional context, serve a function similar to that of vitamins. Minerals may include chemical elements, particularly metallic ones, such as calcium or iron, as well as some compounds.

ORGANIC:

At one time chemists used the term organic only in reference to living things. Now the word is applied to compounds containing carbon and hydrogen.

PROTEINS:

Large molecules built from long chains of amino acids. Proteins serve the functions of promoting normal growth, repairing damaged tissue, contributing to the body's immune system, and making enzymes.

TISSUE:

A group of cells, along with the substances that join them, that form part of the structural materials in plants oranimals.

VITAMINS:

Organic substances that, in extremely small quantities, are essential to the nutrition of most animals and some plants. In particular, vitamins work with enzymes in regulating metabolic processes; however, they do not in themselves provide energy, and thus vitamins alone do not qualify as a form of nutrition.

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Vitamins

Encyclopedia of Food and Culture
COPYRIGHT 2003 The Gale Group Inc.

VITAMINS

Overview

The word "vitamin" came from the term vita mines (vital amines), which was introduced by Casimir Funk, who, in 1912, isolated a growth factor from rice polishings that contained an amine (a compound incorporating a nitrogen atom with two hydrogen atoms) and could cure the disease beriberi. Several other growth factors were identified early in the twentieth century as well, and these substances were also called vitamins even though they did not contain an amine. Vitamins are classified into two major groups: fat-soluble and water-soluble. (See the Appendix for a complete chart of vitamins.)

Fat-Soluble Vitamins

Vitamin A. In the early 1900s, Sir Frederick Hopkins demonstrated that animals would not grow if lard was provided as a sole dietary lipid. When a small quantity of milk containing fat was added to the diet, the animals thrived. The fat-soluble factor was isolated and designated as vitamin A, later called retinol or retinal; these and similar compounds are referred to as retinoids. Carotenoids, which are essentially two retinoids joined tail to tail, are inactive forms of vitamin A and are called provitamin A. They are converted to vitamin A in the intestine and liver. Vitamin A and carotenoids are absorbed in the chylomicron (a lipoprotein particle that transports lipids from the intestine) fraction and stored in the liver. Some foods such as milk are fortified with vitamin A. Rich sources of carotenoids include carrots, leafy green vegetables, and pink grapefruit.

Vitamin A is, chemically, a subgroup of retinoids, which are defined as a class of compounds that consist of a six-membered ring and a side chain with four conjugated double bonds (four isoprenoid units). The term vitamin A is used to describe retinoids exhibiting qualitatively the biologic activity of the retinoid, retinol.

Vitamin A binds to a retinol-binding protein that transports the light-sensitive vitamin to various target tissues, including the eyes, skin, and gastrointestinal track. The major functions of vitamin A include vision and regulation of cellular proliferation and differentiation. Vitamin A functions on vision by interacting with the rod and cone cells in the retina. It is responsible for absorbing light. The 11-cis form of vitamin A (retinal) combines with the protein opsin to form rhodopsin in the rod cells and iodopsins in the cone cells. The rhodopsin and iodopsins absorb light at various wavelengths and trigger a nerve impulse to the visual cortex in the brain that is ultimately perceived as black-and-white and color vision, respectively.

Vitamin A's other major physiologic function is to maintain the health of skin and mucous-secreting cells by regulating their cellular activity and maturation. The dietary requirements depend on age.

The major consequence of vitamin A deficiency, which continues to be a serious nutritional problem among millions of schoolchildren in southern and southeastern Asia and parts of Africa and South America, is night blindness. Vitamin A deficiency can lead to complete blindness and severe damage to the outer covering of the eye (the cornea), often causing it to perforate, with loss of the fluid from inside the eye (keratomalacia). Vitamin A deficiency also produces changes in the skin that are related to the inability of the skin cells to mature and produce keratin properly. This leads to follicular hyperkeratosis and phrynoderma (a condition characterized by rough, dry skin). Vitamin A deficiency has also been linked to increased mortality in early childhood.

Acute and chronic ingestion of excessive amounts of vitamin A can cause a multitude of symptoms and consequences. The most serious is that it can cause severe birth defects, spontaneous abortions and learning defects, and skin and epithelial-cell exfoliation. Inexperienced white explorers of the Arctic who ate polar-bear liver in excess developed severe vitamin A intoxication that caused a total sloughing of their skin and mucoussecreting cells in the upper airway and esophagus, bringing on painful death. (This is in contrast to the indigenous Inuit, who specifically avoid eating polar-bear liver.)

Vitamin D. One of the consequences of the industrial revolution was the high incidence of the bone-deforming disease rickets. It was estimated, at the turn of the twentieth century, that more than ninety percent of children living in the industrialized cities of northern Europe and the northeastern United States had rickets. It had been known that cod-liver oil possessed a factor that had antirachitic activity. Originally, it was thought that the antirachitic factor was vitamin A. However, Hopkins heated cod-liver oil to destroy the vitamin A activity and demonstrated that it still possessed antirachitic activity. This new fat-soluble vitamin was labeled vitamin D. It was also recognized that exposure of food, animals, and humans to ultraviolet radiation also prevented and cured rickets.

There are two principal forms of vitamin D: Vitamin D 2 comes from the precursor ergosterol found in yeast and plants, and vitamin D 3 comes from the cholesterol precursor 7-dehydrocholesterol that is found in the skin of reptiles, birds, mammals, and humans. Vitamin D 2 and vitamin D 3 are essentially equally active in most birds and in most mammals, including humans. Chickens and New World monkeys, however, cannot utilize vitamin D 2. There are very few foods that naturally contain vitamin D. Fatty fish, such as salmon and mackerel, and fish-liver oils, such as cod-liver oil are good sources of vitamin D. Cow's milk and human milk have very little vitamin D. However, in the United States and Canada, milk and some breads and cereals are fortified with vitamin D. In Europe, fortification of foods with vitamin D was outlawed when sporadic cases of vitamin D intoxication were observed in children in the 1950s. Today
some margarine and cereals are fortified with vitamin D in Europe, but milk is not.

Vitamin D 3 is made by the action of sunlight on the skin. Provitamin D 3 (7-Dehydrocholesterol) absorbs solar ultraviolet B radiation (wavelengths 290–315 nm) and is transformed into previtamin D 3. Previtamin D 3 is unstable at body temperature and isomerizes (rotates its double bonds) to vitamin D 3. Once formed, vitamin D 3 leaves the skin and enters the circulation, bound to the vitamin D binding protein. It travels to the liver where it is activated to 25-hydroxyvitamin D [25(OH)D]. This form, however, is biologically inert at physiologic concentrations and is the major circulating form of vitamin D. It is, nevertheless, the form that is measured to determine the vitamin D status of an individual, because it represents a summation of dietary and skin sources of vitamin D. 25(OH)D is transported on the vitamin D binding protein to the kidney, where it undergoes its final activation on carbon 1 to form 1,25-dihydroxyvitamin D [1,25(OH) 2D], the biologically active form of vitamin D.

The principal function of vitamin D is to maintain blood calcium and phosphorus in the normal range in order to promote neuromuscular function and to maintain metabolic activities. It accomplishes this by enhancing the efficiency of intestinal calcium transport in the small intestine and by stimulating precursor cells of osteoclasts to become mature osteoclasts. Among the functions of osteoclasts is to remove calcium from bone. Serum calcium and phosphorus are in the form of Ca x(PO 4). When these compounds are in the normal range, they are in a supersaturated state that can thus be deposited in the skeletal matrix as calcium hydroxyapatite.

1,25(OH) 2D interacts with a receptor in the nucleus of cells, known as the VDR (vitamin D receptor). It also complexes with the "retinoic acid x" receptor in that cellular structure. These receptor-activated vitamin D complexes find their way to genes that have responsive elements known as the vitamin D-responsive element. These elements in turn unlock genetic information that is responsible for various biologic functions in intestine and bone. It is recognized that a wide variety of tissues including the brain, parathyroid glands, breast, pro state, stomach, and skin also have VDR. Although the exact physiologic function of 1,25(OH) 2D in these non-calcium-regulating tissues is not well understood, 1,25(OH) 2D inhibits cellular proliferation and induces terminal differentiation of a wide variety of cells, including bone, skin, skeletal muscle, breast, and prostate. The dietary requirement depends on age.

Vitamin D deficiency results in a decrease in the efficiency of intestinal calcium absorption that in turn leads to a decrease in unbound or free calcium concentrations in the circulation. This is recognized by the parathyroid gland and results in an increase in the production and secretion of parathyroid hormone (PTH). PTH enhances calcium reabsorption by the kidney and causes increased output of phosphate in the urine. PTH also stimulates the kidney to produce more 1,25(OH) 2D. The net effect of vitamin D deficiency is a low-normal serum calcium and a low serum phosphorus (due to the PTH-induced phosphate wasting in the kidney). Thus calcium and phosphorus concentrations fall below supersaturating levels, thereby resulting in poorly mineralized bone. In children, this causes rickets and, in adults, osteomalacia. In addition, vitamin D deficiency in adults can precipitate and exacerbate osteoporosis. In winter, little if any vitamin D can be made in the skin of people who live above 40° north or below 40° south of the equator. An increase in the zenith angle of the sun due to latitude, time of day, and season of the year will dramatically reduce the production of vitamin D 3 in the skin. Moreover, aging and sunscreen use can markedly reduce the production of vitamin D by more than 60 percent and 99 percent, respectively. Rickets due to vitamin D deficiency in children may include bowlegs or knock-knees, widening of the ends of the long bones, growth retardation, and muscle weakness. In adults, in addition to osteomalacia and increased risk of osteoporosis, it causes bone pain, muscle weakness, and fractures.

The safe upper limit for Vitamin D is 2,000 units a day. Although it is difficult to ingest enough to cause vitamin D intoxication, it can occur. Usually, oral ingestion of 10,000 units a day and greater will cause vitamin D intoxication. This intoxication causes an elevation in the blood levels of calcium and phosphorus, which results in the calcification of soft tissues, including the kidney and major blood vessels, and may also cause the formation of kidney stones.

Vitamin E. The discovery of vitamin E (tocopherols—from toc- meaning 'childbirth', phero- meaning 'bringing forth', and -ol representing the alcohol portion of the molecule) was due to the observation that supplementation of the diet with vitamin E prevented fetal death in animals that were fed a diet containing rancid lard. There are eight naturally occurring vitamin E compounds. Four of them are known as tocopherols and four are known as tocotrienols. The most abundant form of vitamin E is alpha-tocopherol. One of the major functions of vitamin E is to act as a biologic antioxidant to protect the sensitive cellular membranes from oxidative destruction. The major sources of vitamin E consumed by Americans are vegetables and seed oils, such as corn oil, soybean oil, and safflower oil. Wheat germ is a rich source of vitamin E. Although butter contains very little vitamin E, American margarine contains a significant amount of this antioxidant vitamin.

Vitamin E, like the other fat-soluble vitamins, is absorbed in the chylomicron fraction into the lymphatic system and is transported into the venous blood. The dietary requirements depend on age.

There have been difficulties in defining a clinical syndrome that correlates with vitamin E deficiency in humans. Vitamin E deficiency is associated with anemia in newborns.

Toxicity from excess vitamin E has been associated with increased bleeding tendency in adults and impaired immune function, decreased levels of vitamin K-dependent clotting factors, and impairment of leukocyte function.

Vitamin K. Vitamin K was discovered by Henrik Dam in Copenhagen in 1929. He observed that chicks fed a fat-free diet developed severe bleeding under the skin and in the muscle and other tissues. He named this new fatsoluble vitamin, vitamin K (for "Koagulation vitamin"). Vitamin K is distributed widely in both animal and vegetable foods as well as in milk. It comes in several forms: vitamin K 1 comes from plants and is known as phylloquinone, and vitamin K 2, first isolated from fish meal and in animal foods, comprises a group of compounds known as menaquinones. In addition, bacterial flora in the intestine synthesize menaquinones that are bioavailable.

Vitamin K, like other fat-soluble vitamins, is absorbed in the chylomicron fraction and then appears in the lymph and subsequently in the venous circulation. The major physiologic function of vitamin K is to activate blood-clotting proteins. This is accomplished by the modification of a substance, glutamate, found in several precoagulant factors, including factors II, VII, VIIII, and X, that are produced in the liver. Vitamin K is also re sponsible for the modification of other proteins, including the major noncollagenous protein in bone. The dietary requirements depend on age.

Vitamin K deficiency is rare because of the widespread distribution of the vitamin in plant and animal foods and because microbiotic flora in the normal gut synthesize menaquinones. However, vitamin K deficiency in breast-fed newborns remains a major worldwide cause of infant morbidity and mortality. Infants have very little stored vitamin K at birth, and the gut is nearly sterile during the first few days of life. As a result, infants can develop a severe bleeding condition known as hemorrhagic disease of the newborn if they do not obtain vitamin K during the first few days of life from an exogenous source, particularly since mother's milk contains little vitamin K and few bacteria other than those it picks up from maternal skin as an infant suckles. Adults who have intestinal malabsorption syndrome and who are taking antibiotics can become severely vitamin K-deficient. This can lead to generalized bleeding from all orifices.

There are no reported cases of intoxication due to excessive ingestion of phylloquinone. Ingestion of excessive amounts of menadione, a vitamin K precursor, can cause anemia secondary to the destruction of red blood cells, and an alteration in bilirubin metabolism causing hyperbilirubinemia in infants (kernicterus).

Water-Soluble Vitamins

Thiamine (vitamin B1). Beriberi is a disease with a constellation of systems affecting the nervous and cardiovascular systems. It was first described by the Chinese in 2697 b.c.e. In 1926, B. C. P. Jansen and W. F. Donath identified a factor from rice-bran extracts that prevented beriberi. The antiberiberi factor was identified chemically and called thiamine (vitamin B1). Thiamine is found in yeast, lean pork, and legumes. It serves as a receptor for high-energy pyrophosphate. It is this form of the vitamin that provides its chemical function. Pyrophosphate is extremely important for the generation of energy in the cell. However, it cannot enter the cell unless it is attached to thiamine. Thiamine is absorbed by the small intestine and transported to the liver. The major biochemical function of thiamine is to act as a coenzyme (that is, to provide a transfer site) in the alpha-keto acid carboxylation pathway. The dietary requirements depend on age.

Thiamine deficiency causes beriberi. Anorexia, neuritis, gastrointestinal dysfunction, cardiac irregularities, and muscle atrophy are present. There are three types of this disorder: wet, dry, and infantile. Wet beriberi is associated with body fluid retention (edema). Dry beriberi is related to neurologic abnormalities. It is recognized that alcoholics who have poor nutrition and thiamine deficiency, when receiving intravenous fluids, for example in the emergency room of a hospital, can develop severe altered mental states known Wernicke's and Korsakoff's syndromes. Wet beriberi is associated with heart abnormalities; dry beriberi is associated with neurological abnormalities that can cause permanent confusion if not treated in a timely manner.

Excessive ingestion of thiamine is cleared by the kidneys. There is no evidence that ingesting excessive amounts causes toxicity.

Riboflavin. In the 1920s, another water-soluble vitamin was discovered; it exhibited antipellagra activity and was termed vitamin B2. The substance was found to be yellow in color and was identified as a coenzyme, riboflavin 5'-phosphate (flavin mononucleotide or FMN).

The more abundant form of this vitamin is a complex flavin-adenine dinucleotide (FAD) that also participates as a coenzyme. Usually, the FMN and FAD are associated loosely with proteins and are released in the acidic gastrointestinal juices. The vitamin is absorbed by the proximal small intestine. Sources of riboflavin include eggs, lean meats, milk, broccoli, and enriched breads and cereals.

The physiologic function of riboflavin is to participate in oxidation-reduction reactions in numerous metabolic pathways and in energy production via the respiratory chain in the mitochondria. The dietary requirements depend on age.

Riboflavin is distributed widely in foodstuffs, and therefore deficiency is not common. However, there are reported cases of deficiency that are characterized by sore throat, hyperemia and edema of the pharyngeal and oral mucosal membranes, cheilosis (abnormal scaling and fissuring of the lips), angular stomatitis (surface inflammation
of the mouth), glossitis (inflammation of the tongue), seborrheic dermatitis (an inflammation of the skin involving oversecretion by the oil-producing cutaneous glands), and anemia. Severe riboflavin deficiency can affect the conversion of vitamin B6 to its coenzyme and reduce the conversion of tryptophan, an amino acid found in proteins of animal and plant origin, to niacin (see next section). Deficiency is principally due to abnormal digestion, abnormal absorption, or both. People who are lactose-intolerant—a condition that is most common among blacks and Asians—often limit consumption of milk (as noted above, an excellent source of riboflavin); they may therefore be at increased risk for riboflavin deficiency. Intestinal malabsorption syndromes, including tropical sprue celiac disease, small bowel resection, and gastrointestinal and biliary obstruction can lead to riboflavin deficiency.

There is no evidence that toxicity can occur as a result of excessive ingestion of riboflavin. The most likely reason for this is that riboflavin is cleared rapidly by the kidney and is not stored in the body.

Niacin. In the mid-1700s, a Spanish physician, Gaspar Casal, recognized a disease known as pellagra that caused diarrhea, dementia, and dermatitis in maize-eating (corneating) populations throughout the world. In 1937, Conrad Elvehjem and his colleagues observed that nicotinic acid was an effective treatment for pellagra. Nicotinic acid is synonymous with both niacin and nicotinamide. It is associated with ribose lyphosphate to form nicotinamide adenine dinucleotide (NAD) and NAD phosphate. Most niacin in food is present as a component of NAD or NADP and is relatively stable to cooking and storage. Good sources of niacin include meats (especially liver), fish, legumes such as peanuts, some nuts, and some cereals. Both coffee and tea also contain reasonable amounts of this vitamin. Niacin is unique among the B vitamins because its precursor amino acid, tryptophan, can help meet the daily niacin requirement.

Niacin has a multitude of physiologic functions in a wide variety of metabolic pathways that are related to energy production and biosynthetic processes. At least two hundred enzymes are dependent on NAD and NADP. Both of these substances act as electron acceptors or hydrogen donors. Most NAD-dependent enzymes are involved in catabolic reactions, whereas NADP is used more commonly for reductive biosyntheses of fatty acids and steroids, for example. The dietary requirements depend on age.

Niacin deficiency causes pellagra. This condition is associated with diarrhea, dementia, and dermatitis. It is endemic in India and in parts of China and Africa. The classic appearance of pellagra is a pigmented rash that develops symmetrically in areas of the skin exposed to sunlight. The tongue can become bright red and there is often vomiting and diarrhea. Patients can also exhibit anxiety or sleeplessness, and can become disoriented and delusional.

Nicotinic acid is now used to treat hypercholesterolemia. Side effects of large amounts of nicotinic acid include flushing of the skin, abnormalities in liver function, and hyperglycemia. At extremely high ingestion levels, nicotinamide causes death in rats.

Pyridoxine (vitamin B6 ). Vitamin B6 was identified in the 1930s. Like many of the water-soluble B vitamins, vitamin B6 includes a group of compounds that act as a coenzyme phosphate donor. These include pyridoxal 5>-phosphate (PLP), and pyridoxamine 5>-phosphate (PMP). Plants foods contain predominantly pyridoxine, whereas animal products contain primarily pyridoxal and pyridoxamine. Vitamin B6 is absorbed mainly by the lower small intestine (jejunum).

Like many of the other coenzyme B vitamins, vitamin B6 has numerous biologic functions that are related to metabolism. B6 is critically important for the production of glucose. PLP is also necessary for the conversion of tryptophan to niacin, which is why the two are often associated. The dietary requirements depend on age.

As with many of the other B vitamins, there are a wide variety of clinical symptoms associated with vitamin B6 deficiency including an abnormal electroencephalogram, convulsions, stomatitis, cheilosis, glossitis, irritability, depression, and confusion.

High doses of pyridoxine have been used to treat premenstrual syndrome and other neurological diseases. Such uses have resulted in neurotoxicity and photosensitivity.

Pantothenic acid. Pantothenic acid was one of the more difficult vitamins to isolate and separate from the other water-soluble B vitamins. Finally in the 1940s, it was synthesized and was found to be associated with coenzyme A (CoA). CoA is an essential cofactor for biologic acetylation reactions and participates in the respiratory tricarboxcylic acid cycle, fatty-acid synthesis and degradation, and a wide variety of other metabolic and regulatory processes. The dietary requirements depend on age.

Pantothenic acid deficiency affects the adrenal gland, nervous system, skin, and hair adversely. Pantothenic acid deficiency in humans is rare, but has been associated with fatigue and depression.

High doses of calcium pantothenate have not been found to be toxic in humans.

Folic acid and cobalamin (vitamin B12 ). In the mid-1800s, several physicians recognized that a severe form of anemia was associated with disorders of the digestive system. In 1934, William Castle and his associates observed that normal human gastric juice contained an intrinsic factor (IF) that combines with an extrinsic factor in animalprotein food, resulting in the absorption of a vitamin that
prevents anemia. Vitamin B12 was isolated in 1948 and was shown to be the extrinsic antianemia factor.

Vitamin B12 absorption is unique among the B vitamins, in requiring an IF to help its absorption. Folate, on the other hand, is absorbed directly by the upper (proximal) small intestine.

Whereas vitamin B12 is found only in animal protein, folates are common in nature and present in nearly all natural foods. The dietary requirements depend on age.

Vitamin B12 deficiency can occur either because of inadequate vitamin B12 ingestion or because of the loss or inadequacy of production of intrinsic factor in the stomach. The two most notable clinical signs of vitamin B12 deficiency include megaloblastic anemia and neurological deficits. Vitamin B12 deficiency can cause paresthesia (especially numbness and tingling in the hands and feet); the diminution of vibration and position sense; unsteadiness; poor muscular coordination with ataxia (loss of muscular coordination); moodiness; mental slowness; poor memory; confusion; agitation; depression; and central visual loss. Delusions, overt psychosis, and paranoid ideas may occur in severe deficiency.

Folate deficiency also causes megaloblastic anemia and can cause neurological abnormalities as well, including irritability, forgetfulness, and hostile and paranoid behavior. For adults, ingestion of ten thousand times the minimum requirement for B12 and several hundred times that for folic acid has not been associated with toxicity.

Biotin. Biotin was identified in the 1940s. It, like many of the other B vitamins, acts as a coenzyme. Biotin is plentiful in foods such as liver, egg yolk, soybeans, yeast, cereals, legumes, and nuts. With the exception of cauliflower and mushrooms, vegetables, fruits, and meats, however, are poor sources of biotin. Biotin is also present in human and cow's milk. The major physiologic functions of biotin are related to carbohydrate and lipid metabolism. The dietary requirements depend on age.

Biotin deficiency causes mental-status changes, myalgia (muscle pain), hyperesthesia (abnormal sensitivity to pain, touch, cold, etc.), localized paresthesia, and anorexia with nausea. Dermatitis can also be associated with deficiency. The immune system is impaired in biotin-deficient animals. Neurological disorders including seizures and developmental delays have been reported in children. There have been no reports of intoxication due to excessive biotin ingestion.

Vitamin C. Scurvy is recognized as a deficiency disease that has taken a high toll in human suffering and death. The disease, which is caused by vitamin C deficiency, was recognized in ancient times by the Egyptians, Greeks, and Romans. It was especially prevalent among sea explorers of the sixteenth to eighteenth centuries. Typically, sailors developed bleeding and rotting gums, swollen and inflamed joints, dark blotches on the skin, and muscle weakness that occurred within months when at sea. It was the loss of 1,051 sailors in 1774 that prompted the British Admiralty to seek a cure for this devastating disease. They found that lemon or lime juice could prevent the disease. In the late 1920s, Albert Szent-Györgyi and Glenn King isolated vitamin C and identified it as hexuronic acid. Vitamin C is water-soluble and is absorbed efficiently by the small intestine. Its major physiologic function is to provide reducing activity for a wide variety of metabolic steps. It is important for the modification of lysine and proline—two amino acids that are common components of collagen. These modifications result in the cross-linking of collagen strands providing structural support for this essential component of bone and fibrous tissues. The dietary requirements depend on age.

As noted, vitamin C deficiency causes scurvy, which is associated with a wide variety of abnormalities, including hemorrhages under the skin, black-and-blue marks, hyperkeratosis, joint discomfort, edema, weakness, fatigue, lassitude, depression, and hysteria.

It was suggested by the Nobel Prize Laureate Linus Pauling that extremely high doses of vitamin C could prevent cancer. With the exception of excessive amounts of vitamin C causing bowel impaction via a large number of vitamin C tablets ingested, there are very few serious consequences from an overingestion of vitamin C, though it can increase the risk of kidney stones and other renal diseases.

Other nutrients. Other nutrients that are essential could be considered vitamins. These include choline, carnitine, inositol, and taurine.

Vitamin/Nutritional Deficiency

Vitamin/nutritional deficiency

Definition

Vitamins are substances that the human body requires but is unable to synthesize and therefore, must obtain externally. Deficiencies in three B vitamins, B1 or thiamine, B3 or niacin and B12 or cobalamin are known to cause neurological disorders. Thiamine deficiencies result in a disease called beriberi , which causes peripheral neurological dysfunction and cerebral neuropathy. Niacin deficiencies cause a wasting disease known as pellagra, which affects the skin, mucous membranes, gastrointestinal tract as well as the brain, spinal cord and peripheral nerves. Cobalamin deficiencies most often result in the disease pernicious anemia. Neurological symptoms of pernicious anemia include numbness in the extremities, impaired coordination and a ringing in the ears.

Description

Thiamine deficiency

Thiamine was the first water-soluble vitamin to be discovered, and is therefore, also known as vitamin B1. Thiamine deficiency, or beriberi, manifests itself as both wet beriberi, which affects the cardiovascular system, and dry beriberi, which causes neurological dysfunction. People suffering from beriberi exhibit muscle atrophy or wasting (especially in the legs), edema (swelling), mental confusion, intestinal discomfort and an enlarged heart. Severe cases of dry beriberi may result in Wernicke-Korsakoff syndrome and acute cases of wet beriberi may cause shoshin beriberi. Both of these extreme forms of the disease are sometimes fatal. In most cases, administering thiamine successfully reverses symptoms associated with thiamine deficiencies.

Niacin deficiency

Niacin deficiency results in a disease called pellagra. The major symptoms of pellagra include dermatitis, dementia (loss of intellectual functions) and diarrhea. Pellagra means rough skin in Italian and it was named because of the characteristic roughened skin of people who have the disease. Skin lesions generally appear on both sides of the body (bilaterally) and are found in regions exposed to sunlight. The disease also affects mucous membranes of the mouth, vagina, and urethra. Gastrointestinal discomfort is an early symptom, followed by nausea, vomiting, and diarrhea, often bloody. Neurological dysfunctions associated with niacin deficiencies include memory loss, confusion and confabulation (imagined memory). Although treatment with niacin usually reverses all of the symptoms, untreated niacin deficiencies can result in multiple organ failure.

Vitamin B12 deficiency

Vitamin B12, also called cobalamin or cyanocobalamin, has the most complex chemical structure of all vitamins. It is unique in that it contains a cobalt atom embedded in a ring, similar to the iron atom in hemoglobin. The cobalt gives the molecule a dark red color. Vitamin B12 is found bound to animal protein and is very rare in vegetables. A deficiency of vitamin B12 results in a blood disorder, also called an anemia, which enlarges red blood cells so that the immune system destroys them at an increased rate. Because the blood cells are enlarged, the disease is characterized as a macrocytic anemia. Vitamin B12 functions in many important cellular processes including synthesis of red blood cells, DNA synthesis and the formation of the myelin sheath that acts as insulation around nerve cells. One of the most common causes of vitamin B12 deficiency is pernicious anemia. Pernicious anemia is caused by a lack of a glycoprotein called intrinsic factor that is required for absorption of vitamin B12. Intrinsic factor is secreted by the stomach, where it binds to the vitamin and transports it to the small intestine for absorption. Symptoms of vitamin B12 deficiency progress from weakness and fatigue to neurological disorders including numbness in the extremities, poor coordination, and eventually, to hallucinations and psychosis. Vitamin B12 deficiencies are usually treated with intramuscular injections of vitamin B12 initially and oral vitamin B12 supplements on an ongoing basis.

Demographics

Thiamine deficiency

Thiamine deficiencies have no sex or racial predilection. Thiamine deficiency is more common in developing countries where poor nutrition occurs frequently, although no accurate statistics on its occurrence are available. In many of these countries, cassava or milled rice acts as a major staple of the diet. While cassava does contain some thiamine, it contains so much carbohydrate relative to the thiamine that eating cassava actually consumes thiamine. Most of the thiamine in rice is found in the husk. When the husk is removed from the rice during milling, the result is a diet staple that is an extremely poor source of thiamine.

Beriberi is often associated with alcoholism, likely because of low thiamine intake, impaired ability to absorb and store thiamine, and acceleration in the reduction of thiamine diphosphate. People who strictly follow fad diets, people undergoing starvation, and people receiving large amounts of intravenous fluids are all susceptible to beriberi. Some physical conditions such as hyperthyroidism, pregnancy, or severe illness may cause a person to require more thiamine than normal and may put a person at risk for deficiency.

A form of beriberi specific to infants known as infantile beriberi can occur in babies between two and four months old that are fed only breast milk from mothers who are thiamine deficient.

Niacin deficiency

Pellagra is most common when maize is a major part of the diet. Although maize does contain niacin, it is not biologically available unless it is treated with basic compounds, such as lime. This process occurs in the making of tortillas, so populations in Mexico and Central America do not usually suffer from pellagra. Maize is also deficient in tryptophan, a precursor to niacin.

In the early 1900s, pellagra was epidemic in the southern United States because of the large amount of corn in the diet. After niacin was discovered to prevent pellagra in 1937, flour was fortified with niacin and reports of pellagra decreased dramatically. Currently, incidence rates of pellagra in the United States are unknown. People at risk for pellagra include alcoholics, people on fad diets, and people with gastrointestinal absorption dysfunction.

The group of people who most commonly suffer from pellagra live in the Deccan Plateau of India. Their diet is rich in millet or sorghum, which contains tryptophan, but also large concentrations of another amino acid, leucine. It is thought that leucine inhibits the conversion of tryptophan to niacin.

Vitamin B12 deficiency

Pernicious anemia is most common in patients of northern European descent and African Americans and less frequent in people of southern European descent and Asians. There is no sex predilection. Vitamin B12 deficiency occurs in 3–43% of people over the age of 65. A form of pernicious anemia is also found in children under the age of ten. It is more frequent in patients with other immune disorders such as Grave's disease or Crohn's disease. There is some evidence that relatives of people who have pernicious anemia are more likely to get the disorder, indicating some genetic component to the disease. Because vitamin B12 only occurs in animal proteins, vegetarians are susceptible to the disease and should take vitamin B12 supplements.

Causes and symptoms

Thiamine deficiency

Thiamine deficiencies are caused by an inadequate intake of thiamine. In most developed countries, getting enough thiamine is not a problem since it is found in all vegetables, especially the outer layer of grains. It is not present in refined sugars or fats and is not found in animal tissue. Diets rich in foods that contain thiaminases, enzymes that break down thiamine, such as milled rice, shrimp, mussels, clams, fresh fish and raw meat may be associated with thiamine deficiencies.

Thiamine is absorbed through the digestive tract by a combination of active and passive absorption. It is stored in the body as thiamine diphosphate, also called thiamine pyrophosphate, and thiamine triphosphate. Thiamine diphosphate is the active form and it is used as a coenzyme in several steps in cellular respiration. Thiamine may also have an important role in the function of nerve cells independent of cellular respiration. It is found in the cell membranes of nerve axons, and electrical stimulation of nerve cells causes a release of thiamine.

Early thiamine deficiency produces fatigue, abdominal pain , constipation, irritation, loss of memory, chest pain, anorexia and sleep disturbance. As the deficiency progresses, it can be classified as dry beriberi or wet beriberi depending on the activity of the patient. Many persons experience a mixture of the two types of beriberi, although pure forms do occur.

When caloric intake and physical activity are low, thiamine deficiency produces neurological dysfunction termed dry beriberi. Symptoms occur with equal intensity on both sides of the body and usually start in the legs. Impaired motor and reflex function coupled with pain, numbness and cramps are symptomatic of the disease. As the disease advances, ankle and knee jerk reactions will be lost, muscle tone in the calf and thigh will atrophy and eventually the patient will suffer from foot drop and toe drop. The arms may begin to show symptoms of neurological dysfunction after the legs are already symptomatic. Histological (tissue) tests may indicate patchy degradation of myelin in muscle tissues.

Wernicke-Korsadoff syndrome, also called cerebral beriberi, occurs in extreme cases of dry beriberi. The early stage is called Korsakoff's syndrome and it is characterized by confusion, the inability to learn, amnesia and telling stories that bear no relation to reality. Wernicke's encephalopathy follows with symptoms of vomiting, nystagmus (rapid horizontal or vertical eye movement), opthalmoplegia (inability to move the eye outwards) and ptosis (eyelid droop). If untreated, Wernicke's encephalopathy may progress to coma and, eventually death.

If a person has a high caloric intake and reasonable levels of activity, but has a diet with insufficient thiamine, myocardial dysfunction termed wet beriberi may result. This disease consists of vasodilatation and high cardiac output, retention of salt and water, and eventual damage to the heart muscle. A person suffering from wet beriberi will exhibit rapid heartbeat (tachycardia), swelling (edema), high blood pressure, and chest pain.

Shoshin beriberi is a more acute form of wet beriberi and it is characterized by damage to the heart muscle accompanied by anxiety and restlessness. If no treatment is received, the damage to the heart may be fatal.

Niacin deficiency

Niacin, also called vitamin B3, is a general term for two molecules: nicotinic acid and nicotinamine. Nicotinic acid is very easily converted into biologically important molecules including nicotinamide adenine dinucleotide (NAD or coenzyme I) and nicotinaminamide adenine dinucleotide phosphate (NADP or coenzyme II), both of which are crucial to oxidation-reduction reactions in cellular metabolism. These reactions play key roles in glycololysis, the generation of high-energy phosphate bonds, and metabolism of fatty acids, proteins, glycerol, and pyruvate. Because niacin plays such an important role in so many different cellular functions, the effect of niacin deficiencies on the body is extremely broad.

The amino acid, tryptophan is a precursor to niacin, and therefore, niacin deficiency can be averted if tryptophan is included in the diet. Some of the psychological symptoms of pellagra are thought to be related to decreased conversion rates of tryptophan to serotonin (a neurotransmitter) in the brain.

Causes of pellagra include diets that are deficient in niacin or its precursor, tryptophan. These diets often rely heavily on unprocessed maize. Other diets that may cause pellagra contain amino acid imbalances. For example, diets that rely on sorghum as a staple contain excessive amounts of the amino acid leucine, which interferes with tryptophan metabolism. Other causes of pellagra include alcoholism, fad diets, diabetes, cirrhosis of the liver, and digestive disorders that prevent proper absorption of niacin or tryptophan. One such disorder is called Hartnup disease, which is a congenital defect that interferes with tryptophan metabolism.

Symptoms of pellagra occur in the skin, in mucous membranes, the gastrointestinal tract, and the central nervous system . Skin symptoms are usually bilaterally symmetric. They include lesions characterized by redness and crusting, thickening of the skin and skin inelasticity. Secondary infections are common, especially after exposure to the sun. Mucus membranes are also affected by pellagra. Typically, the tongue becomes bright red first and then the mouth becomes sore, coupled with increased salivation and edema of the tongue. Eventually, ulcers may appear throughout the mouth. Gastrointestinal symptoms include burning of the mouth, esophagus and abdominal pain. Later symptoms include vomiting and diarrhea, often bloody.

The central nervous system is also affected by niacin deficiencies. Early symptoms include memory loss, disorientation, confusion, hallucination . More severe symptoms are characterized by loss of consciousness, rigidity in the extremities, and uncontrolled sucking and grasping.

Vitamin B12 deficiency

Vitamin B12 is required for the biochemical reaction that converts homocysteine to methionine, one of the essential amino acids required to synthesize proteins. Because vitamin B12 impairs DNA translation, cell division is slow, but the cytoplasm of the cell develops normally. This leads to enlarged cells, especially in cells that usually divide quickly, like red blood cells. In addition, there is usually a high ration of RNA to DNA in these cells. Enlarged red blood cells are more likely to be destroyed by the immune system in the bone marrow, causing a deficit of red blood cells in the blood. Methionine is also required to produce choline and choline-containing phospholipids. Choline and choline-containing phospholipids are a major component of cell membranes and acetocholine, which is crucial to nerve function.

Vitamin B12 requires several binding proteins in order to be absorbed properly. After ingestion into the stomach, it forms a complex with R binding protein, which moves into the small intestine. The stomach secretes another protein, intrinsic factor, which binds with vitamin B12 after R binding factor is digested in the small intestine. Intrinsic factor bound with vitamin B12 adheres to specialized receptors in the ileum, where it is brought inside of cells that line the intestinal wall. Vitamin B12 is then transferred to another protein, transcobalamin II, which circulates through the blood plasma to all parts of the body. Another protein, transcobalamin I, is found bound to vitamin B12; however its function is not well understood.

Because of the complexity of the steps required for vitamin B12 absorption, there are many different ways that deficiencies could arise. First, a person could have inadequate intake of vitamin B12. This is extremely rare, since it is found in most animal proteins, but it does occur in some strict vegetarians. If any of the proteins that usher vitamin B12 through the body are unavailable or damaged, vitamin B12 deficiencies could arise. The most common such problem is associated with inadequate production of intrinsic factor, which results in pernicious anemia. Inadequate production of intrinsic factor can occur because of atrophy (wasting) of the stomach lining, the removal of the part of the stomach that produces intrinsic factor, or in rare cases, because of a congenital defect. Rare cases of intestinal parasites such as a fish tapeworm and bacterial infections may also result in vitamin B12 deficiencies. Finally, acid is often required to hydrolyze vitamin B12 from animal proteins in the stomach. If the stomach is not sufficiently acidic, for example in the presence of antacid medicines, quantities of vitamin B12 available for absorption may be deficient.

The liver stores large amounts of vitamin B12. It is estimated that if vitamin B12 uptake is suddenly stopped, it would take three to five years to completely deplete the stores in a typical adult. As a result, vitamin B12 deficiencies develop over many years. Initial symptoms include weakness, fatigue, lightheadedness, weight loss, diarrhea, abdominal pain, shortness of breath, sore mouth and loss of taste, and tingling in the fingers and toes.

As the disease progresses, neurological symptoms begin to appear. These include forgetfulness, depression , confusion, difficulty thinking, and impaired judgment. Eventually, a person with vitamin B12 deficiency will have numbness in the fingers and toes, impaired balance and poor coordination, ringing in the ears, changes in reflexes, hallucinations, and psychosis.

Diagnosis

Thiamine deficiency

A patient with bilateral symmetric neurological symptoms, especially in the lower extremities may be suffering from thiamine deficiency, especially if there is an indication that the diet may be poor. Some diseases with symptoms that are similar to beriberi include diabetes and alcoholism. Other neuropathies, such as sciatica , are often not symmetric and are not usually associated with beriberi.

Laboratory tests may show high concentrations of pyruvate and lactate in the blood and low concentrations of thiamine in the urine. Because the disease responds so well to thiamine, it is often used as a diagnostic tool. After administration of thiamine diphosphate, an increase in certain enzyme activity in red blood cells is an excellent indicator of thiamine deficiency.

Niacin deficiency

There are no diagnostic tests currently available to detect niacin deficiencies. Concentrations of niacin and tryptophan in the urine of patients suffering from pellagra are low, but not lower than other patients with malnutrition. Diagnosis must be made given a patient's symptoms and dietary history. Because replacement of niacin is so effective, it may be used as a diagnostic tool.

Vitamin B12 deficiency

A person suspected of suffering from vitamin B12 deficiency will be subjected to a physical examination along with blood tests. These blood tests will include a complete blood count (CBC). If blood analyses indicate that the red blood cells are enlarged, vitamin B12 deficiency may be diagnosed. Other disorders that exhibit enlarged red blood cells (macrocytes) include alcoholism, hypthyroidism, and other forms of anemia. White blood cells with segmented nuclei also indicate vitamin B12 deficiency. Other blood tests include a vitamin B12 test and folic acid tests. Low concentrations of both may indicate vitamin B12 deficiencies. Elevated levels of homocysteine, methylmalonic acid (MMA) or lactate dehydrogenase (LDH) indicate vitamin B12 deficiencies. Finally tests that indicate the presence of antibodies against intrinsic factor may indicate pernicious anemia.

Once a vitamin B12 deficiency has been established in a patient, the severity of the disease can be evaluated using a Schilling test. The patient is orally administered radioactive cobalamin and then an injection of unlabeled cobalamin is given intramuscularly. The ratio of radioactive to unlabeled cobalamin in the urine during the next 24 hours gives information on the absorption rate of cobalamin by the patient. If the rates are abnormal, pernicious anemia is diagnosed. As a final check, the patient is given cobalamin bound to intrinsic factor. With this, the patient's absorption rates should become normal if pernicious anemia is the cause of the symptoms.

Treatment

Thiamine deficiency

In most cases, rapid administration of intravenous thiamine will reduce symptoms of thiamine deficiency. Continued dosages of the vitamin should be continued for several weeks accompanied by a nutritious diet. Following recovery, a diet containing one to two times the recommended daily allowance of thiamine (1-1.5 mg per day) should be maintained. Shoshin beriberi requires cardiac support as well. Thiamine has not been found to be toxic for people with normal kidney function, even at high doses.

Niacin deficiency

Niacin deficiency can be treated effectively with replacement of niacin in the diet. In the case of Hartnup disease, large quantities of niacin may be required for effective reversal of symptoms.

Vitamin B12 deficiency

Vitamin B12 deficiency responds well to administration of cobalamin. Because absorption in the small intestine is often part of the problem, the best way to administer cobalamin is by intramuscular injection on a daily basis. After 6 weeks, the injections can be decreased to monthly for the rest of the patient's life. Usually, response to this treatment alleviates all symptoms of the disease. In severe cases, a blood transfusion may be needed and neurological conditions may not be completely reversed.

vitamin

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

vitamin, group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes. A substance that functions as a vitamin for one species does not necessarily function as a vitamin for another species. The vitamins differ in structure, and there is no chemical grouping common to them all.

They were first called accessory factors because in 1906 it was found by English biochemist Sir F. G. Hopkins that most foods contain—besides carbohydrates, proteins, fats, minerals, and water—other substances necessary for health. The word vitamin was derived from the term vitamine, used by Polish-American biochemist Casimir Funk to describe an amine (organic base) that was essential to life (it was later found to be thiamine). In 1912 Hopkins and Funk formulated the vitamin hypothesis of deficiency disease; that is, that certain diseases are caused by a dietary lack of specific vitamins.

The chemical structures of the vitamins are all known, and all of them have been synthesized; the vitamins in foods are identical to the synthetic ones. A well-balanced diet usually satisfies the minimum vitamin requirements of human beings. The Recommended Dietary Allowance (RDA) of each vitamin is the standard guideline put forward by the Food and Nutrition Board, National Academy of Sciences–National Research Council. It is based on the nutritional needs of an average, healthy person. Different amounts may be recommended for children, older people, lactating mothers, or people dealing with an ongoing disease process. The U.S. RDA was the federal government's interpretation of the National Research Council's RDA. Since mid-1994, the U.S. RDA has been replaced on food labels by a Percent Daily Value (the percentage of the U.S. RDA that the labeled food offers). Listings for vitamins A and C are required; others are optional.

The amount of each vitamin that should be consumed for optimal health and the wisdom of taking vitamin supplements, especially in
"megadoses,"
is a controversial question. The Dietary Supplement Health and Education Act of 1994 defined vitamins as dietary supplements (rather than drugs) and shifted the burden of proof of safety from the manufacturers to the Food and Drug Administration. Although vitamins were previously seen only as preventives against the various deficiency diseases, more and more studies have examined additional health benefits of vitamins. Health claims that are unsubstantiated by scientific study, however, are regarded by many health and nutrition experts as fraudulent or dangerous, and many physicians now question the need for healthy persons to take multivitamin supplements, because many foods, such as milk and bread, are fortified with vitamins.

Vitamins were originally classified according to their solubility in water or fats, and as more and more were discovered they were also classified alphabetically. The fat-soluble vitamins are A, D, E, and K; the B complex and C vitamins are water soluble. A group of substances that decrease blood capillary fragility, called the vitamin P group, are no longer considered to be vitamins.

Vitamin A

Vitamin A (retinol), a fat-soluble lipid, is either derived directly from animal foods such as liver, egg yolks, cream, or butter or is derived from beta-carotene, a pigment that occurs in leafy green vegetables and in yellow fruits and vegetables. Vitamin A is essential to skeletal growth, normal reproductive function, and the health of the skin and mucous membranes. One form, retinal, is a component of visual purple, a photoreceptor pigment in the retina of the eye (see vision). In addition, beta-carotene, like other carotenoids, is now recognized as an important antioxidant.

A deficiency of vitamin A can cause retarded skeletal growth, night blindness, various abnormalities of the skin and linings of the genitourinary system and gastrointestinal tract, and, in children, susceptibility to serious infection. The eye disorders that result from a deficiency of vitamin A can lead to permanent blindness. Severe deficiency can cause death. As with the other fat-soluble vitamins, conditions that lead to an inability to absorb fats, such as obstruction of bile flow or excessive use of mineral oil, can produce a deficiency state. Overconsumption of vitamin A can cause irritability, painful joints, growth retardation, liver and spleen enlargement, hair loss, and birth defects. The National Research Council recommended daily dietary allowance for adults is 1,000 micrograms (retinol equivalents) for men and 800 micrograms for women.

Thiamine (vitamin B1 or antiberiberi factor) is a necessary ingredient for the biosynthesis of the coenzyme thiamine pyrophosphate; in this latter form it plays an important role in carbohydrate metabolism. Good sources are yeast, whole grains, lean pork, nuts, legumes, and thiamine-enriched cereal products. This vitamin is a factor in the maintenance of appetite, normal intestinal function, and in the health of the cardiovascular and nervous systems. A deficiency of the vitamin may lead to beriberi; the disease was first shown to result from a dietary deficiency by Dutch physician Christiaan Eijkman. The recommended dietary allowance for adults is 1.2 to 1.4 mg for men and 1.0 to 1.1 mg for women.

Riboflavin

Riboflavin (vitamin B2 or lactoflavin) is used to synthesize two coenzymes that are associated with several of the respiratory enzymes of plants and animals (including humans) and is therefore important in biochemical oxidations and reductions. Deficiency leads to fissures in the corners of the mouth, inflammation of the tongue showing a reddish purple coloration, skin disease, and often severe irritation of the eyes. The recommended dietary allowance for adults is 1.4 to 1.7 mg for men and 1.2 to 1.3 mg for women. Riboflavin is widely distributed in plant and animal tissues; milk, organ meats, and enriched cereal products are good sources.

Niacin

The B vitamins niacin (nicotinic acid) and niacinamide (nicotinamide) are commonly known as preventives of pellagra, which in 1912 was shown by American medical researcher Joseph Goldberger to result from a dietary deficiency. Niacin was first synthesized in 1867. The amino acid tryptophan is the precursor of niacin. Niacin and niacinamide function in the biochemistry of humans and other organisms as components of the two coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP); these operate in many enzyme-catalyzed oxidation and reduction reactions. The deficiency state in humans causes skin disease, diarrhea, dementia, and ultimately death. The deficiency state in dogs analogous to pellagra in humans is called blacktongue disease. Lean meats, peanuts and other legumes, and whole-grain or enriched bread and cereal products are among the best sources of niacin. The recommended daily dietary allowance for adults is 16 to 19 mg niacin equivalents (60 mg of dietary tryptophan to 1 mg of niacin) for men and 13 to 14 mg for women.

Vitamin B6 Group

Pyridoxine, pyridoxal, and pyridoxamine make up the vitamin B6 group. They all combine with phosphorus in the body to form the coenzyme pyridoxal phosphate, which is necessary in the metabolism of amino acids, glucose, and fatty acids. The best sources of B6 vitamins are liver and other organ meats, corn, whole-grain cereal, and seeds. Deficiency can result in central nervous system disturbances (e.g., convulsions in infants) due to the role of B6 in serotonin and gamma-aminobutyric acid synthesis. More generally the effects of deficiency include inadequate growth or weight loss and anemia due to the role of B6 in the manufacture of hemoglobin. The recommended dietary allowance for adults is 2.0 to 2.2 mg for men and 2 mg for women. Additional doses are required in pregnancy and by those taking oral contraceptives or the tuberculosis drug izoniazid. Severe nerve damage has been reported from megadoses.

Pantothenic Acid

Pantothenic acid, another B vitamin, is present in perhaps all animal and plant tissues, as well as in many microorganisms. Good sources of it include liver, kidney, eggs, and dairy products. It is a component of the important substance coenzyme A, which is involved in the metabolism of many biochemical substances including fatty acids, steroids, phospholipids, heme, amino acids, and carbohydrates. The adrenal gland is an important site of pantothenic acid activity. There is no known naturally occurring deficiency state and no known toxicity to pantothenic acid. The estimated safe and adequate daily intake for adults is 4 to 7 mg.

Biotin

Biotin is a B vitamin that functions as a coenzyme in the metabolism of carbohydrates, fats, and amino acids. Although it is vitally necessary to the body, only exceedingly small quantities are needed, and since biotin is synthesized by intestinal bacteria, naturally occurring biotin deficiency disease is virtually unknown. The disease state can be produced artificially by including large quantities of raw egg white in the diet; the whites contain avidin, a biotin antagonist. Especially good sources of this widely distributed vitamin include egg yolk, kidney, liver, tomatoes, and yeast. There is no known toxicity to biotin. The estimated safe and adequate daily intake for adults is 100 to 200 micrograms.

Folic Acid

Folic acid (pteroylglutamic acid, folacin, or vitamin B9) occurs abundantly in green leafy vegetables, fruits (e.g., apples and oranges), dried beans, avocados, sunflower seeds, and wheat germ. Derivatives of this vitamin are directly involved in the synthesis of nucleic acids; for this reason cells in the body that are subject to rapid synthesis and destruction are especially sensitive to folic acid deprivation. For example, the retarded synthesis of blood cells in folic acid deficiency results in several forms of anemia, while failure to replace rapidly destroyed cells in the intestinal wall results in a disease called sprue. Inadequate amounts of folic acid in the diet of pregnant women have been strongly associated with neural tube defects (i.e., spina bifida and anencephaly) in newborns; fortification of flours, cornmeal, rice, and pasta (in a manner similar to the fortification of milk with vitamin D) has been required in the United States since 1998. Adequate folic acid also reduces the risk of premature birth. A U.S. study published in 1998 involving 80,000 women showed significant reduction of heart disease among those whose diets included adequate amounts of folate and vitamin B6. Several chemical antagonists to the action of folic acid have been developed in the hope that they might inhibit the growth of rapidly dividing cancer cells; one such compound, methotrexate, is used to treat leukemia in children. The recommended daily dietary allowance for adults is 400 micrograms. Para-aminobenzoic acid (PABA), which is incorporated into the folic acid molecule, is sometimes listed separately as a B vitamin, although there is no evidence that it is essential to the diet of humans.

Vitamin B12

The molecular structure of vitamin B12 (cobalamin), the most complex of all known vitamins, was announced in 1955 by several scientists, including British biochemists A. R. Todd and Dorothy Hodgkin. In 1973 the vitamin was reported to have been synthesized by organic chemists. Vitamin B12 and closely related cobalamins are necessary for folic acid to fulfill its role; both are involved in the synthesis of proteins. American physicians G. R. Minot and W. P. Murphy in 1926 fed large amounts of liver to patients with pernicious anemia and cured them; the curative substance in this case was probably vitamin B12. However, pernicious anemia in humans is caused not by a vitamin B12 deficiency in the diet but rather the absence of a substance called the intrinsic factor, ordinarily secreted by the stomach and responsible for facilitating the absorption of B12 from the intestine. When a person's body cannot produce the intrinsic factor, the standard treatment today is to inject vitamin B12 directly into the bloodstream. Minot and Murphy's therapy worked because the liver they fed their patients contained such large quantities of B12 that sufficient amounts of the vitamin were absorbed without the assistance of the intrinsic factor. Inadequate absorption of B12 causes pernicious anemia, nervous system degeneration, and amenorrhea. The only site of cobalamin synthesis in nature appears to be in microorganisms; neither animals nor higher plants are capable of making these vitamin B12 derivatives. Nevertheless, such animal tissues as the liver, kidney, and heart of ruminants contain relatively large quantities of vitamin B12; the vitamin stored in these organs was originally produced by the bacteria in the ruminant gut. Bivalves (clams or oysters), which siphon microorganisms from the sea, are also good sources. Plants, on the other hand, are poor sources of vitamin B12. The recommended daily dietary allowance for adults is 3 micrograms.

Vitamin C

Vitamin C, or ascorbic acid, a water-soluble vitamin, was first isolated (from adrenal cortex, oranges, cabbage, and lemon juice) in the laboratories of American biochemists Albert Szent-Gyorgyi and Charles King in the years 1928–33. Szent-Gyorgyi found the Hungarian red pepper to be an exceptionally rich source; citrus fruits and tomatoes are also excellent sources. Other good sources include berries, fresh green and yellow vegetables, and white potatoes and sweet potatoes. The vitamin is readily oxidized and therefore is easily destroyed in cooking and during storage. All animals except humans, other primates, guinea pigs, and one bat and bird species are able to synthesize ascorbic acid. Ascorbic acid is necessary for the synthesis of the body's cementing substances: bone matrix, collagen, dentin, and cartilage. It is an antioxidant and is necessary to several metabolic processes. Deficiency of vitamin C results in scurvy, the symptoms of which are largely related to inadequate collagen synthesis and defective formation of intercellular materials. Ascorbic acid is metabolized slowly in humans, and symptoms of scurvy are usually not seen for three or four months in the absence of any dietary vitamin C. The use of megadoses of ascorbic acid to prevent common colds, stress, mental illness, cancer, and heart disease is a continuing subject of research. The recommended daily allowance for adults is 60 mg.

Vitamin D

Vitamin D is a name given to two fat-soluble compounds; calciferol (vitamin D2) and cholecalciferol (vitamin D3). They are now known to be hormones, but continue to be grouped with vitamins because of historical misclassification. Vitamin D3 plays an essential role in the metabolism of calcium and phosphorus in the body and prevents rickets in children. A plentiful supply of 7-dehydrocholesterol, the precursor of vitamin D3, exists in human skin and needs only to be activated by a moderate amount of ultraviolet light (less than a half hour of sunlight) to become fully potent. Rickets is usually caused by a lack of exposure to sunlight rather than a dietary deficiency, although dietary deficiencies can result from malabsorption in the small intestine caused by conditions such as sprue or colitis. Rickets can be prevented and its course halted by the intake of vitamin D2 (found in irradiated yeast and used in some commercial preparations of the vitamin) or vitamin D3 (found in fish liver oils and in fortified milk). Symptoms of vitamin D deficiency in children include bowlegs, knock knees, and more severe (often crippling) deformations of the bones. In adults deficiency results in osteomalacia, characterized by a softening of the bones. Excessive vitamin D consumption can result in toxicity. Symptoms include nausea, loss of appetite, kidney damage, and deposits of insoluble calcium salts in certain tissues. The recommended daily dietary allowance for cholecalciferol is 15 to 20 micrograms (600 to 800 IU) depending upon age and the availability of sunlight. Fortified cow's milk supplies 400 IU per quart (422 IU per liter).

Vitamin E

Vitamin E occurs in at least eight molecular forms (tocopherols or tocotrienols); in humans the most biologically active form has generally been considered to be alpha-tocopherol, which is also the most common. All forms exist as light yellow, viscous oils. The best sources are vegetable oils. Other sources include green leafy vegetables, wheat germ, some nuts, and eggs. Vitamin E is necessary for the maintenance of cell membranes. It is essential to normal reproduction in some animals, but there is no evidence that it plays a role in human reproduction. It is a potent antioxidant; numerous studies have pointed to a protective effect against arterial plaque buildup and cancer. It is helpful in the relief of intermittent claudication (calf pain) and in preventing problems peculiar to premature infants. In large doses, it has an anticoagulant effect. The recommended daily dietary allowance for adults is 10 mg (tocopherol equivalents) for men and 8 mg for women, but nutritionists and physicians sometimes recommend higher doses for disease prevention.

Vitamin K

Vitamin K consists of substances that are essential for the clotting of blood. It was identified in 1934 by Danish biochemist Henrik Dam. Two types of K vitamins have been isolated: K1, an oil purified from alfalfa concentrates, and K2, synthesized by the normal intestinal bacteria. Both can be derived from the synthetic compound menadione (sometimes called vitamin K3), a yellow crystalline solid that is as potent in its ability to promote blood clotting as the natural vitamins. The best sources are leafy green vegetables, such as cabbage and spinach, and intestinal bacteria (which produce most of the body's supply of vitamin K). Vitamin K is required for the synthesis in the liver of several blood clotting factors, including prothrombin. Coumarin derivatives, used in medicine to prevent blood coagulation in certain cases, act by antagonizing the action of vitamin K. In the deficiency state an abnormal length of time is needed for the blood to clot, and there may be hemorrhaging in various tissues. Deficiency occurs in hemorrhagic disease of the newborn infant, in liver damage, and in cases where the vitamin is not absorbed properly by the intestine. It can also occur in coumarin therapy or when normal intestinal bacteria are destroyed by extended antibiotic therapy. Vitamin K does not treat hemophilia. Deficiency is rarely of dietary origin. The estimated safe and adequate intake for adults is 70 to 140 micrograms.

Vitamin

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Vitamin

Vitamins are complex organic compounds that occur naturally in plants and animals. People and other animals need these compounds in order to maintain life functions and prevent diseases. About 15 different vitamins are necessary for the nutritional needs of humans. Only minute amounts are required to achieve their purpose, yet without them life cannot be maintained. Some vitamins, including vitamins A, D, E, and K, are fat soluble and are found in the fatty parts of food and body tissue. As such they can be stored in the body. Others, the most notable of which are vitamin C and all the B-complex vitamins, are water soluble. These vitamins are found in the watery parts of food and body tissue and cannot be stored by the body. They are excreted in urine and must be consumed on a daily basis.

History

Vitamins were not discovered until early in the twentieth century. Yet it was common knowledge long before that time that substances in certain foods were necessary for good health. Information about which foods were necessary developed by trial and error—with no understanding of why they promoted health. Scurvy, for example, had long been a dreaded disease of sailors. They often spent months at sea and, due to limited ways of preserving food without refrigeration, their diet consisted of dried foods and salted meats. In 1746, English naval captain and surgeon James Lind (1716–1794) observed that 80 out of his 350 seamen came down with scurvy during a 10-week cruise. He demonstrated that this disease could be prevented by eating fresh fruits and vegetables during these long periods at sea. Because they lasted a long time, limes became the fruit of choice. In 1795, lemon juice was officially ordered as part of the seaman's diet. The vitamin C found in both limes and lemons prevented scurvy in sailors.

In 1897, Dutch physician Christian Eijkman (1858–1930) found that something in the hulls of rice (thiamine, a B vitamin) not present in the polished grains prevented the disease beriberi (a disease that affects the nerves, the digestive system, and the heart). Soon after, British biochemist Frederick G. Hopkins (1861–1947) fed a synthetic diet of fats, carbohydrates, proteins, and minerals (but no vitamins) to experimental rats. The rats showed poor growth and became ill, leading Hopkins to conclude that there were some "accessory food factors" necessary in the diet. Eijkman and Hopkins shared the 1929 Nobel Prize in physiology and medicine for their important work on vitamins.

Words to Know

Antioxidant: A substance that can counteract the effects of oxidation.

Beriberi: A disease caused by a deficiency of thiamine and characterized by nerve and gastrointestinal disorders.

Carbohydrate: A compound consisting of carbon, hydrogen, and oxygen found in plants and used as a food by humans and other animals.

Deficiency diseases: Diseases caused by inadequate amounts in the diet of some substance necessary for good health and the prevention of disease.

Fat-soluble vitamins: Vitamins such as A, D, E, and K that are soluble in the fatty parts of plants and animals.

Pellagra: A disease caused by a deficiency of niacin and characterized by severe skin problems and diarrhea.

Proteins: Large molecules that are essential to the structure and functioning of all living cells.

Scurvy: A disease caused by a deficiency of vitamin C, which causes a weakening of connective tissue in bone and muscle.

Water-soluble vitamins: Vitamins such as C and the B-complex vitamins that are soluble in the watery parts of plant and animal tissues.

Finally, in 1912, Polish American biochemist Casimir Funk (1884–1967) published a paper on vitamin-deficiency diseases. He coined the word vitamine from the Latin vita, for "life," and amine, because he thought that all of these substances belonged to a group of chemicals known as amines. The e was later dropped when it was found that not all vitamins contained an amine group. Funk identified four vitamins (B1 or thiamine, B2, C, and D) as substances necessary for good health and the prevention of disease.

Since that time additional vitamins have been isolated from foods, and their relationship to specific diseases have been identified. All of these accessory food factors have been successfully synthesized in the laboratory. There is no difference in the chemical nature of the natural vitamins and those that are made synthetically, even though advertisements sometimes try to promote natural sources (such as vitamin C from rose hips) as having special properties not present in the synthesized form.

Nature of vitamins

Vitamins belong to a group of organic compounds required in the diets of humans and other animals in order to maintain good health: normal growth, sustenance, reproduction, and disease prevention. In spite of their importance to life, they are necessary in only very small quantities. The total amount of vitamins required for one day weigh about one-fifth of a gram. Vitamins have no caloric value and are not a source of energy.

Vitamins cannot be synthesized by the cells of an animal but are vital for normal cell function. Certain plants manufacture these substances, and they are passed on when the plants are eaten as food. Not all vitamins are required in the diets of all animals. For example, vitamin C is necessary for humans, monkeys, and guinea pigs but not for animals able to produce it in their cells from other chemical substances. Nevertheless, all higher animals require vitamin C, and its function within organisms is always the same.

Vitamins were originally classified into two broad categories according to their solubilities in water or in fat. As more vitamins were discovered, they were named after letters of the alphabet. Some substances once thought to be vitamins were later removed from the category when it was found that they were unnecessary or that they could be produced by an animal. Four of the better known vitamins, A, D, E, and K, are fat soluble. Other vitamins such as vitamin C and the B-complex vitamins are water soluble.

This difference in solubility is extremely important to the way the vitamins function within an organism and in the way they are consumed. Fat-soluble vitamins lodge in the fatty tissues of the body and can be stored there. It is, therefore, not necessary to include them in the diet every day. Because these vitamins can be stored, it also is possible (when consumed in excess) for them to build up to dangerous levels in the tissues and cause poisoning.

The Food and Drug Administration publishes a set of nutritional recommendations called the U.S. Recommended Dietary Allowances (USRDA) patterned on the needs of the average adult. These recommendations are based on the best information available but are less than perfect; most of the research upon which they are determined is done on experimental animals. Because the amounts of vitamins required are so small, precise work is very difficult.

A person who eats a balanced diet with plenty of fresh fruits and vegetables should receive adequate amounts of all the vitamins. Many vitamins, however, are very sensitive to heat, pressure cooking, cold, and other aspects of food preparation and storage and can be inactivated or destroyed.

A controversy about vitamins exists among experts regarding the dose needed to fight off some common diseases. According to these experts, the USRDA are really minimum requirements, and higher doses will keep a person healthier. Thus, many people worldwide take vitamin supplements as insurance that they are getting all they need. Overdosage on vitamins, especially the fat-soluble ones, can cause serious side effects, however, and in some cases they even interfere with the proper function of other nutrients.

Vitamin A

Vitamin A is present in animal tissue, mainly in liver, fish oil, egg yolks, butter, and cheese. Plants do not contain vitamin A, but they do contain beta carotene, which is converted to vitamin A in the intestine and then absorbed by the body. Beta carotene occurs most commonly in dark green leafy vegetables and in yellowish fruits and vegetables such as carrots, sweet potatoes, cantaloupe, corn, and peaches. The bodies of healthy adults who have an adequate diet can store several years' supply of this vitamin. But young children, who have not had time to build up such a large reserve, suffer from deprivation more quickly if they do not consume enough of the vitamin.

Vitamin A is necessary for proper growth of bones and teeth, for the maintenance and functioning of skin and mucous membranes, and for the ability to see in dim light. There is some evidence that it can help prevent cataracts and cardiovascular disease and, when taken at the onset of a cold, can ward it off and fight its symptoms. One of the first signs of a deficiency of this vitamin is night blindness, in which the rods of the eye (necessary for night vision) fail to function normally. Extreme cases of vitamin A deficiency can lead to total blindness. Other symptoms include dry and scaly skin, problems with the mucous linings of the digestive tract and urinary system, and abnormal growth of teeth and bones.

Vitamin A is stored in the fatty tissues of the body and is toxic in high doses. As early as 1596, Arctic explorers experienced vitamin A poisoning. In this region of extreme conditions, the polar bear was a major source of their food supply, and a quarter pound of polar bear liver contains about 450 times the recommended daily dose of vitamin A. Excessive amounts of vitamin A cause chronic liver disease, peeling of the skin of the entire body, bone thickening, and painful joints. However, it is nearly impossible to ingest beta carotene in toxic amounts since the body will not convert excess amounts to toxic levels of vitamin A.

Vitamin D

Vitamin D is often called the sunshine vitamin. It is produced when compounds that occur naturally in animal bodies are exposed to sunlight. Thus, it is difficult to suffer a vitamin D deficiency if one gets enough sunshine. One form of vitamin D is often added to milk as an additive. Storage and food preparation do not seem to affect this vitamin.

Vitamin D lets the body utilize calcium and phosphorus in bone and tooth formation. Deficiency of this vitamin causes a bone disease called rickets. This disease is characterized by bone deformities (such as bowlegs, pigeon breast, and knobby bone growths on the ribs where they join the breastbone) and tooth abnormalities. In adults, bones become soft and porous as calcium is lost.

Excessive amounts of vitamin D cause nausea, diarrhea, weight loss, and pain in the bones and joints. Damage to the kidneys and blood vessels can occur as calcium deposits build up in these tissues.

Vitamin E

Vitamin E is present in green leafy vegetables, wheat germ and other plant oils, egg yolks, and meat. The main function of this vitamin is to act as an antioxidant, particularly for fats. (When oxidized, fats form a very reactive substance called peroxide, which is often very damaging to cells. Vitamin E is more reactive than the fatty acid molecule and, therefore, takes its place in the oxidizing process.) Because cell membranes are partially composed of fat molecules, vitamin E is vitally important in maintaining the nervous, circulatory, and reproductive systems and in protecting the kidneys, lungs, and liver.

All of the symptoms of vitamin E deficiency are believed to be due to the loss of the antioxidant protection it offers to cells. This protective effect also keeps vitamin A from oxidizing to an inactive form. And when vitamin E is lacking, vitamin A deficiency also frequently occurs. However, because vitamin E is so prevalent in foods, it is very difficult to suffer from a deficiency of this vitamin unless no fats are consumed in the diet. When it does occur, the symptoms include cramping in the legs, muscular dystrophy, and fibrocystic breast disease.

According to some current theories, many of the effects of aging are caused by the oxidation of fat molecules in cells. If this is true, then consuming extra vitamin E might counteract these effects because of its antioxidant properties.

Vitamin K

Vitamin K is found in many plants (especially green leafy ones like spinach), in liver, and in the bacteria of the intestine. Nearly all higher animals must obtain the vitamin K they need from these sources. Although the exact method by which vitamin K works in the body is not understood, it is known that vitamin K is vital to the formation of prothrombin—one of the chemicals necessary for blood clotting—found in the liver.

When vitamin K deficiency develops, it is rarely due to an incomplete diet. Instead, it results from liver damage and the blood's inability to process the vitamin. The deficiency is characterized by the inability of the blood to clot, and it manifests in unusual bleeding or large bruises under the skin or in the muscles. Newborn infants sometimes suffer from brain hemorrhage due to a deficiency of vitamin K.

Vitamin B

What was once thought to be vitamin B was later found to be only one of many B vitamins. Today, more than a dozen B vitamins are known, and they are frequently referred to as vitamin B-complex. Thiamine was the first of these vitamins to be identified. All of the B vitamins are water soluble.

Each of the B vitamins acts by combining with another molecule to form an organic compound known as a coenzyme. A coenzyme then works with an enzyme to perform vital activities within the cell. The function of enzymes within a cell vary, but all are somehow related to the release of energy. The most common members of this group of vitamins include vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B6 (pyridoxine), vitamin B12 (cobalamin), biotin, folate (also folacin or folic acid), niacin, and pantothenic acid.

Vitamin B1 is present in whole grains, nuts, legumes, pork, and liver. It helps the body release energy from carbohydrates. More than 4,000 years ago, the Chinese described a disease we know today as beriberi, which is caused by a deficiency of thiamine. The disease affects the nervous and gastrointestinal system and causes nausea, fatigue, and mental confusion. Thiamine is found in the husks or bran of rice and grains. Once the grain is milled and the husks removed, rice is no longer a source of this vitamin. Manufacturers today produce enriched rice and flour by adding thiamine back into the milled products.

Vitamin B2 helps the body release energy from fats, proteins, and carbohydrates. It can be obtained from whole grains, organ meats, and green leafy vegetables. Lack of this vitamin causes severe skin problems. Vitamin B6 is important in the building of body tissue as well as in protein metabolism and the synthesis of hemoglobin. A deficiency can cause depression, nausea, and vomiting. Vitamin B12 is necessary for the proper functioning of the nervous system and in the formation of red blood cells. It can be obtained from meat, fish, and dairy products. Anemia, nervousness, fatigue, and even brain degeneration can result from vitamin B12 deficiency.

Niacin is required to release energy from glucose. It is present in whole grains (but not corn), meat, fish, and dairy products. Inadequate amounts of this vitamin cause a disease called pellagra, which is characterized by skin disorders, weak muscles, diarrhea, and loss of appetite. Pellagra was once common in Spain, Mexico, and the southeastern United States, where a large component of the diet consisted of corn and corn products. The niacin in corn exists as part of a large, fibrous molecule that cannot be absorbed by the blood or used by the body. However, after it was discovered that treating corn with an alkaline solution (such as lime water) releases the niacin from the larger molecule and makes it available for the body to use, pellagra became much less common.

Pantothenic acid helps release energy from fats and carbohydrates and is found in large quantities in egg yolk, liver, eggs, nuts, and whole grains. Deficiency of this vitamin causes anemia. Biotin is involved in the release of energy from carbohydrates and in the formation of fatty acids. It is widely available from grains, legumes (peas or beans), egg yolk, and liver. A lack of biotin causes dermatitis (skin inflammation).

Vitamin C

Because of its association with the common cold, vitamin C (also known as ascorbic acid) is probably the best known of all the vitamins. Most animals can synthesize this vitamin in the liver, where glucose is converted to ascorbic acid. Humans, monkeys, guinea pigs, and the Indian fruit bat are exceptions and must obtain the vitamin from their diets. The vitamin is easily oxidized, and food storage or food processing and preparation frequently destroy its activity. Soaking fruits and vegetables in water for long periods also removes most of the vitamin C. Citrus fruits, berries, and some vegetables like tomatoes and peppers are good sources of vitamin C.

The exact function of vitamin C in the body is still not well understood, but it is believed to be necessary for the formation of collagen, an important protein in skin, cartilage, ligaments, tendons, and bone. It also plays a role in the body's absorption, use, and storage of iron. Vitamin C is an antioxidant and is therefore believed to offer protection to cells much as vitamin E does. An increasing body of evidence suggests that a greatly increased amount of vitamin C in the diet lessens the risk of heart disease and cancer.

A deficiency of vitamin C causes a disease called scurvy. Scurvy weakens the connective tissue in bones and muscles, causing bones to become very porous and brittle and muscles to weaken. As the walls of the circulatory system become affected, sore and bleeding gums and bruises result from internal bleeding. Anemia can occur because iron, which is critical to the transport of oxygen in the blood, cannot be utilized. Vitamin C is metabolized (broken down) very slowly by the body, and deficiency diseases do not usually manifest themselves for several months.

Linus Pauling (1901–1994), the winner of two Nobel Prizes (one for chemistry and one for peace), believed that massive doses of vitamin C could ward off the common cold and offer protection against some forms of cancer. While scientific studies have been unable to confirm this theory, they do suggest that vitamin C can at least reduce the severity of the symptoms of a cold. Some studies also suggest that vitamin C can lessen the incidence of heart disease and cancer. If this is true, it could be that the antioxidant properties of the vitamin help protect cells from weakening and breaking down much as vitamin E does. In fact, vitamins A, C, and E all play similar roles in the body, and it is difficult to distinguish among their effects.

[See alsoMalnutrition; Nutrition ]

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Vitamin

How Products Are Made
COPYRIGHT 1996 Gale Research Inc.

Vitamin

Background

Vitamins are organic compounds that are necessary in small amounts in animal and human diets to sustain life and health. The absence of certain vitamins can cause disease, poor growth, and a variety of syndromes. Thirteen vitamins have been identified as necessary for human health, and there are several more vitamin-like substances that may also contribute to good nutrition. Originally, it was thought that vitamins were particular chemical compounds called amines, but now it is known that the vitamins are unrelated chemically. Their actions are different, and though exhaustively studied, not everything is understood about how they work and what they do. The vitamins are named by letters—vitamin A, vitamin C, D, E, K, and the group of B vitamins. The eight B vitamins were originally thought to be one vitamin, and as more was learned about them, they were given numeral subscripts: vitamin B,, B2, etc. The B vitamins are now commonly called more aptly by chemically descriptive names: B, is thiamine, B2 is riboflavin, B6 and B12 retain their numeral names, and the other B vitamins are niacin, pantothenic acid, biotin, and folic acid. The vitamins are found in plant and animal food sources. They have also been chemically synthesized and so can be ingested in their pure form as nutritional supplements. It is not known precisely how much of each vitamin each person needs, but there are recommended daily allowances for 10 vitamins.

Some researchers have made extravagant claims about the benefits of large doses of specific vitamins as either preventatives or cures for diseases from acne to cancer. As new discoveries are made and old claims are either debunked or reinforced often, it is safest to say that more is understood about the consequences of lack of vitamins than what particular vitamins may do. For example, deficiency of vitamin A leads to break-down of the photosensitive cells in the retina of the eye, causing night blindness. Absence of vitamin C in the diet leads to scurvy, a disease formerly the bane of sailors. Absence of vitamin D may lead to rickets, a bone disease.

History

Many researchers were responsible for piecing together the existence of vitamins as necessary components of the human and animal diets. One of the first people to study nutrition from a chemical standpoint was English physician William Prout. In 1827, he defined the three essentials of the human diet as the oily, the saccharin, and the albuminous, which in modern-day terms are fats and oils, carbohydrates, and proteins. In 1906, an English biochemist, Frederick Hopkins, discovered that mice fed on a pure diet of the three essentials could not survive unless they were given supplementary small amounts of milk and vegetables. A Polish scientist, Casimir Funk, coined the term vitamines in 1912 to describe the chemicals he believed were found in the supplementary food that helped the mice survive. Funk first believed that the vitamines were chemically related amines, thus vita (life) plus amines. As other vitamins were isolated that were not amines, the spelling of the word changed. Other researchers working on diseases such as scurvy and beriberi, which are caused by vitamin deficiency, contributed to the isolation
of the different vitamins. Still, little was generally understood about vitamins at the beginning of the twentieth century. For instance, though the use of lime juice to prevent scurvy in sailors dates back to at least 1795, the physician who accompanied Scott's voyage to the South Pole in 1910 believed scurvy was caused by bacteria, and inadequate nutritional measures were taken to prevent the disease among the explorers. Between 1925 and 1955, the known vitamins were all isolated and synthesized. Research continues today on the function of the various vitamins.

Raw Materials

Vitamins can be derived from plant or animal products, or produced synthetically in a laboratory. Vitamin A, for example, can be derived from fish liver oil, and vitamin C from citrus fruits or rose hips. Most commercial vitamins are made from synthetic vitamins, which are cheaper and easier to produce than natural derivatives. So vitamin A may be synthesized from acetone, and vitamin C from keto acid. There is no chemical difference between the purified vitamins derived from plant or animal sources and those produced synthetically. Different laboratories may use different techniques to produce synthetic vitamins, as many can be derived from various chemical reactions.

Vitamin tablets or capsules usually contain additives that aid in the manufacturing process or in how the vitamin pill is accepted by the body. Microcrystalline cellulose, lactose, calcium, or malto-dextrin are added to many vitamins as a filler, to give the vitamin the proper bulk. Magnesium stearate or stearic acid is usually added to vitamin tablets as a lubricant, and silicon dioxide as a flow agent. These additives help the vitamin powder run smoothly through the tablet-making or encapsulating machine. Modified cellulose gum or starch is often added to vitamins as a disintegration agent. That is, it helps the vitamin compound break up once it is ingested. Vitamin tablets are also usually coated, to give the tablets a particular color or flavor, or to determine how the tablet is absorbed (in the stomach versus in the intestine, slowly versus all at once, etc.). Many coatings are made from a cellulose base. An additional coating of carnauba wax is often put on as well, to give the tablet a polished appearance.

Herbs of various kinds may be added to vitamin compounds, as well as minerals such as calcium, iron, and zinc. Typically, specialized laboratories produce purified vitamins and minerals. A distributor buys these from the laboratories and sells them to manufacturers, who put them together in different compounds such as multivitamin tablets or B-complex capsules.

The Manufacturing Process

Preliminary check

1 A vitamin manufacturer purchases raw vitamins and other ingredients from distributors. Raw vitamins from a reputable distributor arrive with a Certificate of Analysis, stating what the vitamins are and how potent they are. In many cases, the manufacturer will nevertheless test the raw materials or send samples to an independent laboratory for analysis. If herbs are to be an ingredient in the vitamin capsule, these must be tested for identity and potency, and for possible bacterial contamination as well.

Preblending

2 Often, the raw vitamins arrive at the manufacturer in a fine powder, and they need no preliminary processing. However, if the ingredients are not finely granulated, they will be run through a mill and ground. Some vitamins may be preblended with a filler ingredient such as microcrystalline cellulose or malto-dextrin, because this produces a more even granule which aids further processing steps. Laboratory technicians may run test batches when working with new ingredients and determine if preblending is necessary.

Wet granulation

3 For vitamin tablets, particle size is extremely important in determining how well the formula will run through the tabletting machine. In some cases, the raw vitamins arrive from the distributor milled to the appropriate size for tabletting. In other cases, a wet granulation step is necessary. In wet granulation, the fine vitamin powder is mixed with a variety of cellulose particles,
then wetted. The mixture is then dried in a dryer. After drying, the formula may be in chunks as large as a dime. These chunks are sized by being run through a mill. The mill forces the chunks through a small hole of the desired diameter of the granule. These granules can then be weighed and mixed.

Weighing and mixing

4 When all the vitamin ingredients are ready, a worker takes them to the weigh station and weighs them out on a scale. The required weights for each ingredient in the batch are listed on a formula batch record. After weighing, the worker dumps all the ingredients into a mixer. The volume of a typical mixer may be from 15-30 cu ft (0.42-0.84 cu m), though in a large manufacturing facility, it may be many times that large. The ingredients spend from 15 to 30 minutes in the mixer. At this point, samples are taken from different sides of the mixer and checked in the laboratory. The lab technicians verify that all the ingredients are distributed in the same proportion throughout the mix. If the manufacturer is making a large batch, workers may check the first three or four lots in the mixer, and then only re-check periodically. After mixing is complete, workers take the vitamin formula to either an encapsulating or a tablet-making machine.

Encapsulating machine

5 If the lot in the mixer has been approved, workers tote the mixture to the encapsulating machine and dump it in a hopper. At the beginning of a batch, workers
will test-run the encapsulating machine and check that the capsules are the proper and consistent weight. Workers also check the capsules visually to see if they seem to be splitting or dimpling. If the test batches run correctly, workers run the entire batch. The vitamin mixture flows through one hopper, and another hopper holds whole gelatin capsules. The capsules are broken into halves by the machine. The bottom half of the capsule falls through a funnel into a rotating dosing dish. Then the machine measures a precise amount of the powdered vitamin mixture into each open capsule half. Tamping pins push the powder down. Then the top halves of the capsules are pushed down onto the filled bottoms.

Polishing and inspection

6 The filled vitamin capsules are next run through a polishing machine. The vitamins are circulated on a belt through a series of soft brushes. Any excess dust or vitamin powder is removed from the exterior of the capsules by the brushes. The polished capsules are then poured onto an inspection table. The inspection table has a belt of rotating rods. The vitamins fall in the grooves between the rods, and the vitamins rotate as the rods turn. Thus, all sides of the vitamin are visible for the inspector to see. The inspector removes any capsules that are too long, split, dimpled, or otherwise imperfect. The vitamins that pass inspection are then taken over to the packaging area.

Tableting

7 Vitamin tablets are made in a tableting machine. After the vitamin blend has been mixed in the mixer, workers dump it into a hopper above the machine. The vitamin powder then flows through the hopper to a filling station beneath, and flows from there to a rotating table. The rotating table may be 2-4 ft (0.6-1.2m) in diameter, or even bigger, and is fitted with holes on its outside edge that hold dies in the shape of the desired tablet (oval, round, animal, etc.).
The dies are interchangeable, so the same table can produce whatever shape the manufacturer wishes, as long as the proper dies are installed. The vitamin powder flows from the filling station to fill the die. When the table rotates, the filled die moves into a punch press. When the upper and lower halves of the punch meet, 4-10 tons (3.6-9 metric tons) of pressure is exerted on the vitamin powder. The pressure compresses the vitamin powder into a compact tablet. The punch releases, and the lower punch lifts to eject the tablet. Some tableting machines may have two punches, one on each side, so two tablets are made simultaneously. The speed of the rotation of the table determines how many tablets are made per minute. The tablets eject onto a vibrating belt which vibrates any loose dust off the tablets. The tablets then are moved to the coating area.

Coating

8 Vitamin tablets are usually coated for a variety of reasons. The coating may make the tablet easier to swallow. It may mask an unpleasant taste, and it may give the tablet a pleasant color. A manufacturer may coat in two different colors tablets that are the same size and shape, for identification. Tablets may also be given an enteric coating—a pH sensitive chemical coating that resists gastric acid. Tablets with an enteric coating will not break open in the stomach, but move to the intestine before dissolving. Other coatings determine the timing of the tablet's dissolution, so the vitamins can be absorbed slowly, or all at once, depending on what is appropriate to that tablet.

Once the tablets are taken from the tableting area, they are placed in the coating pan. The coating pan is a large rotating pan surrounded by one to six spray guns operated by pumps. As the tablets revolve in the pan, the pumps spray coating over them. Many tablets also receive a second coating of carnauba wax. After air drying, the tablets are ready for packaging. The packaging step is the same for tablets as for capsules.

Packaging

9 Packaging the vitamins takes several steps, and different machines carry out these steps. So in the packaging area, the vitamins pass through a row of machines. Once the vitamins are dumped in the hopper of the first machine, no human touches them. The worker sets the machine to count out the required number of capsules or tablets per bottle, and the rest is done automatically. The capsules or tablets fall into a bottle, and the bottle is passed to the next machine to be sealed, capped, labelled, and shrink-wrapped. The finished bottles are then set in boxes and are ready for distribution.

Quality Control

Checks for quality are taken at many stages of vitamin manufacturing. All the ingredients of vitamin tablets or capsules are checked for identity and potency before they are used. Often this is tested both by the raw vitamin distributor and by the manufacturer. The mixed vitamin powder is checked before it is tableted or encapsulated, and the finished product is also thoroughly inspected. Federal regulations govern what substances can be used in vitamins and what claims manufacturers can make for their products. Vitamin ingredients must be proven safe before they can be made available to consumers.

The Future

Vitamin research is a volatile field, with new studies constantly suggesting new roles for vitamins in health and prevention of disease. Certain vitamins or vitamin-like substances go through fads of consumer popularity as some of this research surfaces. Nevertheless, the manufacturing process remains the same for new substances. The future of vitamins will likely change most conceptually, in how much we understand about how vitamins work.

Where to Learn More

Books

Bender, David A. Nutritional Biochemistry of the Vitamins. Cambridge University Press, 1992.

Vitamins

Vitamins

Definition

Vitamins are organic components in food that are needed in very small amounts for growth and for maintaining good health. The vitamins include vitamins D, E, A, and K (fat-soluble vitamins), and folate (folic acid ), vitamin B12, biotin, vitamin B6, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid) (water-soluble vitamins). Vitamins are required in the diet in only tiny amounts, in contrast to the energy components of the diet. The energy components of the diet are sugars, starches, fats, and oils, and these occur in relatively large amounts in the diet.

Most of the vitamins are closely associated with a corresponding vitamin deficiency disease. Vitamin D deficiency causes rickets, a disease of the bones. Vitamin E deficiency occurs only very rarely and causes nerve damage. Vitamin A deficiency, common throughout the poorer parts of the world, causes night blindness. Severe vitamin A deficiency can result in xerophthalmia, a disease that, if left untreated, results in total blindness. Vitamin K deficiency results in spontaneous bleeding. Mild or moderate folate deficiency, common throughout the world, can result from the failure to eat green, leafy vegetables or fruits and fruit juices. Folate deficiency causes megaloblastic anemia, which is characterized by the presence of large abnormal cells called megaloblasts in the circulating blood. The symptoms of megaloblastic anemia are tiredness and weakness. Vitamin B12 deficiency occurs with the failure to consume meat, milk, or other dairy products. Vitamin B12 deficiency causes megaloblastic anemia and, if severe enough, can result in irreversible nerve damage. Niacin deficiency results in pellagra, which involves skin rashes and scabs, diarrhea , and mental depression. Thiamin deficiency results in beriberi, a disease resulting in atrophy, weakness of the legs, nerve damage, and heart failure. Vitamin C deficiency results in scurvy, a disease that involves bleeding. Diseases associated with deficiencies in vitamin B6, riboflavin, or pantothenic acid have not been found in the humans, though persons who have been starving or consuming poor diets for several months, might be expected to be deficient in most of the nutrients, including vitamin B6, riboflavin, and pantothenic acid. Rarely, deficiency in B6 results in neurologic problems. Issues of toxicity are connected to the over consumptions of vitamins, particularly E, K, and B. Also, lack of regulation in the vitamin industry means consumers ought only to buy well-known brands.

Some of the vitamins serve only one function in the body, while other vitamins serve a variety of unrelated functions. Hence, some vitamin deficiencies tend to result in one type of defect, while other deficiencies result in a variety of problems.

Description

Vitamin treatment is usually done in three ways: by replacing a poor diet with one that supplies the recommended dietary allowance, by consuming oral supplements, or by injections. Injections are useful for persons with diseases that prevent absorption of fat-soluble vitamins. Oral vitamin supplements are especially useful for persons who otherwise cannot or will not consume food that is a good vitamin source, such as meat, milk, or other dairy products. For example, a vegetarian who will
not consume meat may be encouraged to consume oral supplements of vitamin B12.

Treatment of genetic diseases which impair the absorption or utilization of specific vitamins may require megadoses of the vitamin throughout one's lifetime. Megadose means a level of about 10 to 1,000 times greater than the RDA. Pernicious anemia, homocystinuria, and biotinidase deficiency are three examples of genetic diseases which are treated with megadoses of vitamins.

General use

People are treated with vitamins for three reasons. The primary reason is to relieve a vitamin deficiency, when one has been detected. Chemical tests suitable for the detection of all vitamin deficiencies are available. The diagnosis of vitamin deficiency is often aided by visual tests, such as the examination of blood cells with a microscope, the x-ray examination of bones, or a visual examination of the eyes or skin.

A second reason for vitamin treatment is to prevent the development of an expected deficiency. Here, vitamins are administered even with no test for possible deficiency. One example is vitamin K treatment of newborn infants to prevent bleeding. Food supplementation is another form of vitamin treatment. The vitamin D added to foods serves the purpose of preventing the deficiency from occurring in persons who may not be exposed much to sunlight and who fail to consume foods that are fortified with vitamin D, such as milk. Niacin supplementation prevents pellagra, a disease that occurs in people who rely heavily on corn as the main source of food and who do not eat much meat or milk. In general, the American food supply is fortified with niacin.

A third reason for vitamin treatment is to reduce the risk for diseases that may occur even when vitamin deficiency cannot be detected by chemical tests. One example is folate deficiency. The risk for cardiovascular disease can be slightly reduced for a large fraction of the population by folic acid supplements. And the risk for certain birth defects can be sharply reduced in certain women by folic acid supplements.

Vitamin treatment is important during specific diseases in which the body's normal processing of a vitamin is impaired. In these cases, high doses of the needed vitamin can force the body to process or use it in the normal manner. One example is pernicious anemia, a disease that tends to occur in middle age or old age and impairs the absorption of vitamin B12. Surveys have revealed that about 0.1 percent of the general population, and 2–3 percent of the elderly, may have the disease. If left untreated, pernicious anemia leads to nervous system damage. The disease can easily be treated with large oral daily doses of vitamin B12 (hydroxocobalamin) or with monthly injections of the vitamin.

Vitamin supplements are widely available as over-the-counter products. But whether they work to prevent or curtail certain illnesses, particularly in people with a balanced diet, is in the early 2000s a matter of debate and ongoing research. For example, vitamin C is not proven to prevent the common cold . Yet millions of Americans take it for that reason. Consumers should ask a physician or pharmacist for more information on the appropriate use of multivitamin supplements.

KEY TERMS

Genetic condition—A condition that is passed from one generation to the next but does not necessarily appear in each generation. Examples of genetic conditions include Down syndrome, Tay-Sach's disease, sickle cell disease, and hemophilia.

Recommended dietary allowance (RDA)—The Recommended Dietary Allowances (RDAs) are quantities of nutrients in the diet that are required to maintain good health in people. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences, and may be revised every few years. A separate RDA value exists for each nutrient. The RDA values refer to the amount of nutrient expected to maintain good health in people. The actual amounts of each nutrient required to maintain good health in specific individuals differ from person to person.

Serum—The fluid part of the blood that remains after blood cells, platelets, and fibrogen have been removed. Also called blood serum.

Vitamin status—The state of vitamin sufficiency or deficiency of any person. For example, a test may reveal that a patient's folate status is sufficient, borderline, or severely inadequate.

The diagnosis of a vitamin deficiency usually involves a blood test. An overnight fast is usually recommended as preparation prior to withdrawal of the blood test so that vitamin-fortified foods do not affect the test results.

The response to vitamin treatment can be monitored by chemical tests, by an examination of red blood cells or white blood cells, or by physiological tests, depending on the exact vitamin deficiency.

Precautions

Vitamin A and vitamin D can be toxic in high doses. Side effects range from dizziness to kidney failure. Consumers should ask a physician or pharmacist about the correct use of a multivitamin supplement that contains these vitamins.

Side effects

Few side effects are associated with vitamin treatment if vitamins are taken within the prescribed dosages. Excessive intake of some B vitamins may impart a greenish color to urine. Any possible risks depend on the vitamin and the reason why it was prescribed. Consumers should ask a physician or pharmacist about how and when to take vitamin supplements, particularly those that have not been prescribed by a physician.

Parental concerns

The dosage of vitamin supplements should not exceed the recommended daily allowance without a recommendation by a physician. Recommended dosages vary with age, so parents should be should to give vitamins to children that are specially formulated for children. Vitamin bottles will list recommended doses for different age groups. Infants and toddlers may also benefit from vitamin supplements if they do not eat a variety of foods. Liquid vitamin supplements are available commercially for these young children.

Vitamins

Gale Encyclopedia of Medicine, 3rd ed.
COPYRIGHT 2006 Thomson Gale

Vitamins

Definition

Vitamins are organic components in food that are needed in very small amounts for growth and for maintaining good health. The vitamins include vitamin D, vitamin E, vitamin A, and vitamin K, or the fat-soluble vitamins, and folate (folic acid), vitamin B12, biotin, vitamin B6, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid), or the water-soluble vitamins. Vitamins are required in the diet in only tiny amounts, in contrast to the energy components of the diet. The energy components of the diet are sugars, starches, fats, and oils, and these occur in relatively large amounts in the diet.

Most of the vitamins are closely associated with a corresponding vitamin deficiency disease. Vitamin D deficiency leads to diseases of the bones such as osteoporosis and rickets. Vitamin E deficiency occurs only rarely, and causes nerve damage. Vitamin A deficiency is common throughout the poorer parts of the world, and causes night blindness. Severe vitamin A deficiency can result in xerophthalamia, a disease which, if left untreated, results in total blindness. Vitamin K deficiency results in spontaneous bleeding. Mild or moderate folate deficiency is common throughout the world, and can result from the failure to eat green, leafy vegetables or fruits and fruit juices. Folate deficiency causes megaloblastic anemia, which is characterized by the presence of large abnormal cells called megaloblasts in the circulating blood. The symptoms of megaloblastic anemia are tiredness and weakness. Vitamin B12 deficiency occurs with the failure to consume meat, milk or other dairy products. Vitamin B12 deficiency causes megaloblastic anemia and, if severe enough, can result in irreversible nerve damage. Niacin deficiency results in pellagra. Pellagra involves skin rashes and scabs, diarrhea, and mental depression. Thiamin deficiency results in beriberi, a disease that can cause atrophy, weakness of the legs, nerve damage, and heart failure. Vitamin C deficiency results in scurvy, a disease that involves bleeding. Specific diseases uniquely associated with deficiencies in vitamin B6, riboflavin, or pantothenic acid have not been found in humans, though persons who have been starving, or consuming poor diets for several months, might be expected to be deficient in most of the nutrients, including vitamin B6, riboflavin, and pantothenic acid.

Some of the vitamins serve only one function in the body, while other vitamins serve a variety of unrelated functions. Therefore, some vitamin deficiencies tend to result in one type of defect, while other deficiencies result in a variety of problems.

Purpose

People are treated with vitamins for three reasons. The primary reason is to relieve a vitamin deficiency, when one has been detected. Chemical tests suitable for the detection of all vitamin deficiencies are available. The diagnosis of vitamin deficiency often is aided by visual tests, such as the examination of blood cells with a microscope, the x-ray examination of bones, or a visual examination of the eyes or skin.

Helps the liver eliminate toxins Promotes the growth and reproduction of body cells; aids in the formation of red blood cells and bone marrow

Vitamin C (Ascorbic Acid)

One of the major antioxidants; essential for healthy teeth, gums, and bones; helps to heal wounds, fractures, and scar tissue; builds resistance to infections; assists in the prevention and treatment of the common cold; prevents scurvy

Vitamin D

Improves the absorption of calcium and phosphorous (essential in the formation of healthy bones and teeth) maintains nervous system

A second reason for vitamin treatment is to prevent the development of an expected deficiency. Here, vitamins are administered even with no test for possible deficiency. One example is vitamin K treatment of newborn infants to prevent bleeding. Food supplementation is another form of vitamin treatment. The vitamin D added to foods serves the purpose of preventing the deficiency from occurring in persons who may not be exposed much to sunlight and who fail to consume foods that are fortified with vitamin D, such as milk. Niacin supplementation prevents pellagra, a disease that occurs in people who rely heavily on corn as the main source of food, and who do not eat much meat or milk. In general, the American food supply is fortified with niacin.

A third reason for vitamin treatment is to reduce the risk for diseases that may occur even when vitamin deficiency cannot be detected by chemical tests. One example is folate deficiency. The risk for cardiovascular disease can be slightly reduced for a large fraction of the population by folic acid supplements. And the risk for certain birth defects can be sharply reduced if certain pregnant women use folic acid supplements.

Vitamin treatment is important during specific diseases where the body's normal processing of a vitamin is impaired. In these cases, high doses of the needed vitamin can force the body to process or utilize it in the normal manner. One example is pernicious anemia, a disease that tends to occur in middle age or old age, and impairs the absorption of vitamin B12. Surveys have revealed that about 0.1% of the general population, and 2-3% of the elderly, may have the disease. If left untreated, pernicous anemia leads to nervous system damage. The disease can easily be treated with large oral daily doses of vitamin B12 (hydroxocobalamin) or with monthly injections of the vitamin.

Vitamin supplements are widely available as over-the-counter products. But whether they work to prevent or curtail certain illnesses, particularly in people with a balanced diet, is a matter of debate and ongoing research. For example, vitamin C is not proven to prevent the common cold. Yet, millions of people take it for that reason. A physician or pharmacist can provide more information on the appropriate use of multivitamin supplements. Likewise, though vitamin supplements have been touted as a prevention for cancer, a 2004 report by the U.S. Preventive Services Task Force concluded that the evidence is inadequate to recommend supplementation of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations to decrease the risk of cancer.

Precautions

Vitamin A and vitamin D can be toxic in high doses. Side effects range from dizziness to kidney failure. A physician or pharmacist can help with the correct use of a multivitamin supplement that contains these vitamins.

Description

Vitamin treatment usually is done in three ways: by replacing a poor diet with one that supplies the recommended dietary allowance, by consuming oral supplements, or by injections. Injections are useful for people with diseases that prevent absorption of fat-soluble vitamins. Oral vitamin supplements are especially useful for people who otherwise cannot or will not consume food that is a good vitamin source, such as meat, milk, or other dairy products. For example, a vegetarian who will not consume meat may be encouraged to consume oral supplements of vitamin B12.

Treatment of genetic diseases that impair the absorption or utilization of specific vitamins may require megadoses of the vitamin throughout one's lifetime. Megadose means a level of about 10-1,000 times greater than the recommended daily allowance (RDA). Pernicious anemia, homocystinuria, and biotinidase deficiency are three examples of genetic diseases that are treated with megadoses of vitamins.

Preparation

The diagnosis of a vitamin deficiency usually involves a blood test. An overnight fast usually is recommended as preparation prior to withdrawal of the blood test so that vitamin-fortified foods do not affect the test results.

Aftercare

Response to vitamin treatment can be monitored by chemical tests, by an examination of red blood cells or white blood cells, or by physiological tests, depending on the exact vitamin deficiency.

Risks

Few risks are associated with supervised vitamin treatment. Risks depend on the vitamin and the reason why it was prescribed. Ask a physician or pharmacist about how and when to take vitamin supplements, particularly those that have not been prescribed by a physician.

PERIODICALS

KEY TERMS

Genetic disease— A genetic disease is a disease that is passed from one generation to the next, but does not necessarily appear in each generation. An example of genetic disease is Down's syndrome.

Plasma— Blood consists of red and white cells, as well as other components, that float in a liquid. This liquid is called plasma.

Recommended dietary allowance (RDA)— The Recommended Dietary Allowances (RDAs) are quantities of nutrients of the diet that are required to maintain human health. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences and may be revised every few years. A separate RDA value exists for each nutrient. The RDA values refer to the amount of nutrient expected to maintain health in the greatest number of people.

Serum— Serum is blood plasma with the blood clotting proteins removed. Serum is prepared by removing blood from the subject, allowing the blood naturally to form a blood clot, and then using a centrifuge to remove the red blood cells and the blood clot. The blood clot takes the form of an indistinct clump.

Vitamin status— Vitamin status refers to the state of vitamin sufficiency or deficiency of any person. For example, a test may reveal that a patient's folate status is sufficient, borderline, or severely inadequate.

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vitamins

vitamins In present day Western society, the small print on packets of cereals and of citrus drinks is a ready source of information on the vitamins they provide, the quantity contained therein, and the fraction which that content provides of the recommended daily allowance (RDA). In many homes there is also a stock of packaged tablets or bottled syrups, swallowed mostly on the principle that if a little of these stuffs is necessary for health, then more must be better. In some instances this may possibly be so, but by no means to the extent that vitamin supplements are sold and bought. A vitamin is an organic substance that is necessary only in very small amounts (RDAs all less than 200 mg) for normal growth and health and which must be obtained from the diet because it cannot be synthesized by the body. But, as with many original definitions of this sort, exceptions have emerged with the progress of research.

There were three diseases that during the eighteenth and nineteenth centuries began to be linked in some way to the diet. The cure of scurvy in a ship's company by provision of citrus fruit dates back to 1754, to a historic, but initially neglected experimental observation: men with the disease were divided into pairs, and each pair given different additions to their rations; those, and only those, who received oranges and lemons recovered. The scurvy was successfully avoided with the issue of fruit and vegetables on Captain Cook's voyages in the 1770s, and official introduction of lemon juice into the Royal Navy diet followed before the end of the century. Understanding of the reason for this was to take more than a century. The occurrence of pellagra started to be associated from the mid 1700s with a poor diet of maize-meal without meat or milk in different parts of the world, and this link was still occurring in the US well into the twentieth century. The condition of beri-beri was prevalent in nineteenth-century Asian workers who lived mainly on rice that had been ‘improved’ by new machinery which removed the husks; also chickens who ate rice without its husks developed a peripheral nerve abnormality like that in the human disease. It was at first assumed that some toxin had been introduced by the cooking or polishing. But husks — or an extract made from them — were later shown to cure the condition in both people and chickens. Thus the notion gradually arose that diseases might be caused by an absence of something, rather than the presence of a poison or infection.

The table shows the main sources of each vitamin, and main features of its deficiency. Most of the names refer to a group of substances with similar action.

The concept of necessary substances in the diet — in addition to the major energy-providers and minerals — whose absence led to disease, entered several minds, and led to many clinical and experimental studies in the early twentieth century. An early pioneer was the British biochemist Frederick Gowland Hopkins, later a Nobel prize winner. He, among others, found that a combination of all known nutrients was not sufficient to allow young animals to thrive. The word ‘vitamine’ was invented in 1911 by Funk, a biochemist also working in London, who believed, rightly, that he had isolated a vital dietary constituent from rice husks — and, wrongly, that it was by chemical nature an amine. Such extracts became known as vitamin B, and the original name without the ‘e’ came to be applied to the family of substances that emerged over the following decades as necessary for health, but required only in very small quantities. In the 1920s ‘vitamin B’ proved to be more than one substance; B1 was identified as the anti-beri-beri factor, and others with comparable properties, equally essential, were later added to the group. Knowledge emerged, thanks to a young American physician, William Castle, of a vitamin (B12) necessary for blood cell production, which needed a gastric secretion to allow its absorption — explaining the empirical observation that very large amounts of raw liver were needed to cure pernicious anaemia. Vitamin C — which prevented scurvy — was finally identified in lemon juice in 1932, was found to be readily destroyed by heat, was given the name of ascorbic acid, and became the first vitamin to be artificially synthesized. Meanwhile, some factor in fish oils and egg yolks became recognized as being necessary for growth and health, and was initially called vitamin A. Extracts proved effective against rickets, and this component was separately labelled vitamin D. Thus by the time of World War II the main vitamins had been identified, and their importance recognized; national programmes such as vitamin additions to staple foods and provision of enriched juices for infants and children supported wartime public health; vitamins had also become a major commercial proposition.

Each vitamin is a requisite for some essential metabolic function, and most cannot be synthesized in the body. The exceptions are vitamin D, which can be made in the skin in the presence of sunlight; vitamin A, which need not as such be in the diet, since it can be made from carotenes present in vegetables; and vitamin K, which can be made by bacteria in the gut.

The naming of the vitamins does not appear very logical, for various historical reasons. They are described in two categories — water-soluble and fat-soluble. The significance of this distinction relates to their sources, their absorption, storage, and excretion, and to the manner of their action.

The water-soluble vitamins comprise vitamin C and the ‘B group’ (see table). Vitamin C is necessary for collagen synthesis, the basis of connective tissue growth and maintenance. Those of the B group act by forming co-enzymes, essential for a range of vital, enzyme-dependent cellular processes. These include DNA synthesis, different components of the utilization of nutrients, and the respiratory and energy-releasing processes. Folic acid and B12 specifically are essential for the formation of normal red blood cells. B12 is unique in requiring the intrinsic factor secreted by glands in the stomach to enable it to be absorbed from the intestine, and also in being obtainable only from animal sources.

The fat-soluble vitamins are A, D, E, and K. Fat-solubility means not only that their sources are in fats in the diet, but also that they can be stored in adipose tissue and can have actions on cells by dissolving in the lipid cell membranes. Deficiency may occur not only in malnutrition, but also in any condition that interferes with fat absorption, including liver disease because of the role of bile. Unlike water-soluble vitamins, their storage means that signs of deprivation are delayed — and also that over-dosage can become toxic.

For many of the vitamins there are distinctive abnormalities related to their deficiency, which can be reversed by an adequate intake. Deficiencies occur in undernourished or malnourished communities or individuals; in alcoholism, poverty, and neglect in the aged in any society; and in strict vegetarians. Apart from the treatment of deficiency conditions, the question remains open, and the subject of research, as to whether there is any advantage to be gained from supplements in excess of the minimal adequate amounts. Since the relatively recent understanding of the damaging effect of free radicals, the counteracting antioxidant action of vitamins A, C, and E has been recognized; the fat-soluble and water-soluble vitamins may combine to protect against free radical damage particularly to cell membranes, and thus to diminish processes such as arteriosclerosis and others associated with ageing. Some of the B vitamins (folic acid and B12) may have a role in protecting from heart disease. There has been contradictory evidence concerning protection from the common cold or alleviation of its symptoms by large doses of vitamin C. On the other hand, there can be serious ill-effects from overdose of the fat-soluble vitamins and also of vitamin C.

Sheila Jennett

Bibliography

Carpenter, K. J. (1986). The history of scurvy and vitamin C. Cambridge University Press. Roe, D. A. (1973). A plague of corn: the social history of pellagra. Cornell University Press, Ithaca NY.

Vitamins

Gale Encyclopedia of Cancer
COPYRIGHT 2002 The Gale Group Inc.

Vitamins

Definition

Vitamins are compounds that are essential in small amounts for proper body function and growth. Vitamins are either fat soluble: A, D, E, and K; or water soluble: vitamin B and C. The B vitamins include vitamins B1 (thiamine), B2 (riboflavin), and B 6 (pyridoxine), pantothenic acid, niacin, biotin, folic acid (folate), and vitamin B 12 (cobalamin). Vitamins may also be referred to as micronutrients.

Description

A guide to the amount an average person needs each day to remain healthy has been determined for each vita-min. In the United States, this guide is called the recommended daily allowance (RDA). Consumption of too little or too much of certain vitamins may lead to a nutrient deficiency or a nutrient toxicity respectively.

Consumption of a wide variety of foods, with adequate vitamin and mineral intake is the basis of a healthy diet. Good nutrition may assist in the prevention of cancer, or for those with existing malignancies, may help cancer patients to feel better and fight infection during treatments. Obtaining nutrients through food remains the best method for obtaining vitamins, however, requirements may be higher because of the tumor or cancer therapy. Therefore supplements may be necessary.

The following vitamins are important in a healthy diet and also may assist in cancer prevention. Their role in maintaining health and best food sources are listed below.

Causes

Specific nutrients have been linked to prevention of several cancers of the colon, breast, prostate, stomach, and other types of tumors. A high intake of fruits and vegetables as well as fiber appears particularly protective, while a diet high in fat has been implicated as a cancer risk.

Vitamins important for cancer prevention

Antioxidant vitamins are believed to protect the body from harmful free radicals that can contribute to diseases such as cancer. Antioxidant vitamins include vitamin A, C, and E. However, doses too high may increase oxidative stress and therefore may be detrimental to cancer risk.

A diet rich in fruits and vegetables (containing B6, folate, and niacin) appears to protect against stomach cancer and in particular, intestinal cancer.

One study reported that cruciferous vegetables, especially broccoli, brussel sprouts, cauliflower, and cabbage were associated with a decreased risk of prostate cancer . Other foods were also associated with a lower risk such as carrots, beans, and cooked tomatoes.

A component of Vitamin E, tocotrienol, has been linked to a decreased risk of breast cancer in lab animals. Tocotrienol has been shown to readily kill tumor cells grown in culture. Tocotrienol is not the same type of substance found in generic Vitamin E supplements, but is plentiful in palm oil. Palm oil is difficult to obtain in the Western world, but lower concentrations of tocotrienol are found in rice bran oil and wheat bran oil.

Researchers state that no single nutrient is the answer, but that the effects are cumulative and depend on eating a variety of fruits and vegetables. Because there are many more nutrients available in foods such as fruits and vegetables than in vitamin supplements, food is the best source for acquiring needed vitamins and minerals.

Special concerns

There are concerns regarding antioxidant levels during chemotherapy and radiation therapy . Researchers report large amounts of Vitamin C are consumed by cancerous tumors during chemotherapy in studies with mice. Vitamin C is an antioxidant that consumes free radicals and is thought to perhaps interfere with the process of killing cancer cells during chemotherapy or radiation therapy. Cancer patients undergoing chemotherapy are advised against taking large amounts of Vitamin C. Another research study has also warned cancer patients about vitamin A and vitamin E during chemotherapy because it has demonstrated a protective effect on cancer cells in mice. These antioxidants may protect not only the normal cells from being destroyed, but also may protect dangerous cancer cells from being destroyed during cancer treatment. The researchers suggest an antioxidant-depleted diet may be prudent during cancer therapy.

Smokers are advised not to consume a diet high in beta-carotene (Vitamin A) because research has shown a link to increased lung cancer incidence.

Alternative and complementary therapies

There are a great many claims about particular vita-min and or antioxidants having beneficial health effects. Proper nutrition with an adequate diet is the best way to obtain vitamins, but a supplement may be required when intake is inadequate. It is important to check with a dietitian or doctor before taking nutritional supplements or alternative therapies because they may interfere with cancer medications or treatments.

Resources

BOOKS

Keane, Maureen, et al. What to Eat If You Have Cancer: A Guide to Adding Nutritional Therapy to Your Treatment Plan. Lincolnwood, IL: National Textbook Company/Contemporary Publishing Group, 1996.

KEY TERMS

Antioxidant

Cancer

—A term for diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread through the bloodstream and lymphatic system to other parts of the body.

Free radicals

—Free radicals are highly reactive chemicals that often contain oxygen. They are produced when molecules are split to give products that have unpaired electrons. This process is referred to as oxidation.

Malignant (also malignancy)

—Meaning cancerous; a tumor or growth that often destroys surrounding tissue and spreads to other parts of the body.

Oxidative stress

—A condition in which antioxidant levels are lower than normal. Antioxidant levels are usually measured in blood plasma.

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Vitamin Tests

Gale Encyclopedia of Medicine, 3rd ed.
COPYRIGHT 2006 Thomson Gale

Vitamin Tests

Definition

Vitamin tests measure the levels of certain vitamins in an individual's blood. They are generally used to aid in the diagnosis of vitamin deficiencies or in detecting toxic amounts of a vitamin in a patient's system.

Purpose

Vitamins are components of food that are needed for growth, reproduction, and maintaining good health. The vitamins include vitamin D, vitamin E, vitamin A, and vitamin K, which are the fat-soluble vitamins, and folate, vitamin B12, biotin, vitamin B6, niacin, thiamin, riboflavin, pantothenic acid, and ascorbic acid, which are the water-soluble vitamins. Vitamins are required in the diet in only tiny amounts, in contrast to the energy components of the diet, such as sugars, starches, and fats. However, not receiving sufficient quantities of a certain vitamin can be devastating, resulting in vitamin deficiency diseases such as scurvy, pellagra, or rickets. Conversely, consuming too much of a certain vitamin can be toxic to a person's system. Vitamin tests are used to assess the level of certain vitamins in an individual's blood so that doctors can more accurately diagnose vitamin deficiency diseases or vitamin overdoses and devise effective therapy. The vitamins that are most commonly measured by doctors are folate, vitamin B12, vitamin K, vitamin D, and vitamin A.

Description

Most of the vitamin tests are conducted by acquiring a sample of blood, and then preparing plasma or serum from the blood sample. Each vitamin occurs at extremely small concentrations when compared to levels of most other molecules in the blood. Blood contains a great number of chemicals and molecules, and many of these tend to interfere with the vitamin tests. For this reason, a procedure that separates the vitamin from contaminating substances is usually performed immediately prior to conducting the actual test. Most laboratories use high pressure liquid chromatography (HPLC), also called high performance liquid chromatography, as this purification step. In HPLC, the sample is pumped at high pressure through a tube lined with an absorbent material, to which the different molecules cling at different rates. Following separation or purification by HPLC, the vitamin is detected by a color reaction or fluorescence reaction. In these reactions, the amount of color or fluorescence that is formed is proportional to the amount of vitamin in the sample, allowing the analyst to calculate the amount of vitamin present in the original sample. In the case of some vitamins, the purified vitamin is reacted with a special chemical (reagent) prior to detection.

Levels of some vitamins may be measured indirectly by a biological test that mimics the actual function of the vitamin in the body. Riboflavin status is often measured by a test in which the rate by which a certain enzyme converts one molecule into another indicates how much Vitamin B2 is present in a person's blood. Vitamin K is often measured by a test that times how long it takes for a spontaneous blood clot to form in a prepared sample. Vitamin E status is often measured by placing the red blood cells in a test tube, adding hydrogen peroxide, and assessing the resulting breakdown of the red blood cells. When a vitamin E deficiency exists, the red blood cells have a greater tendency to break.

Preparation

Most vitamin tests require no preparation; however, some may require that the patient fast for at least eight hours before giving a blood sample, or stop using some medications.

Normal results

The values that are considered to be normal for each vitamin can vary slightly. This variability can arise from different testing machines or from different types of chemistry that are used in conducting the vitamin assays. In interpreting data on plasma vitamin levels, it should also be noted that different normal ranges may exist for different age groups and genders. For example, the normal range for plasma vitamin B6 for males is 7-52 nanograms per milliliter (ng/mL) for males and 2-26 ng/mL for females.

The normal ranges for levels of certain vitamins are as follows. Please note that, by convention, the units referring to the levels of each of the vitamins may differ from each other. The units picogram/milliliter (pg/mL), nanogram/milliliter (ng/mL), and micrograms per deciliter (micrograms/dL) refer to the weight of vitamin in the specified volume. The units nanomoles/liter (nmol/L) and micromoles/liter (M/L) refer to the concentration of vitamin in the specified volume.

folate (folic acid ): 3.1-18.0 ng/mL

vitamin B12: 200-1100 pg/mL

thiamin: 9-44 nmol/L

riboflavin: 6.2-39 nmol/L

vitamin B6: 7-52 ng/mL

vitamin C (asorbic acid): 28-84 M/L

vitamin A: 28-94 micrograms/dL

vitamin D (25-hydroxy-vitamin D): 25-50 ng/mL

vitamin K: 80-1160 pg/mL

Abnormal results

In all cases, abnormal results fall below or above the normal concentration range. However, as noted above, values that are considered to be borderline or severely abnormal can differ according to the discretion of the medical laboratory or physician.

Vitamins

Encyclopedia of Aging
COPYRIGHT 2002 The Gale Group Inc.

VITAMINS

A vitamin is defined as a chemical (organic compound) present in variable small quantities in natural foodstuffs and essential for the normal processes of growth and maintenance of the body. Vitamins do not furnish energy, but are essential for the transfer of energy and regulation of metabolism (chemical processes) involved in the normal growth and maintenance of the body (Parker).

The word vitamin was coined in 1912 by the Polish-born American biochemist Casimir Funk (1884–1967) to describe a ‘‘vital amine’’ from rice husks that cured beriberi, a disease that affects brain and nervous function (Thadani; Horton). Indeed, thiamine or vitamin B1, contains an amine (nitrogen) group. However, the term is a misnomer because not all vitamins contain nitrogen. For example, vitamins A, D, E, and K are not amines and do not contain nitrogen.

What are some common vitamin deficiencies seen with age?

Vitamin deficiencies in older adults may be caused by decreased food intake, changes in taste, smell, hearing and vision, loss of teeth, ongoing illness or medications. For example:

Loss of teeth can result in decreased food intake and a diet favoring a limited number of pre-prepared pureed foods. In these cases, it is important to identify foods that need to be modified in consistency and those that can be eaten as is (for example, fresh bananas) to prevent vitamin deficiencies.

In older adults a diet lacking zinc can contribute to a loss of taste. This can be remedied with a zinc supplement.

Acid production in the stomach slows with age decreasing the amount of iron and vitamin B12 absorbed. This may lead to anemia. Illnesses like ulcer, hemorrhoids, and colon cancer can also cause blood loss leading to anemia. Regular use of aspirin as an anti-inflammatory at higher doses can also cause blood loss in the stomach and contribute to anemia.

A nutritionally balanced diet and routine physical checkups help to prevent disease and maintain health during a lifetime.

What are antioxidants?

Vitamins A, C, and E are often described as antioxidants. They are substances that prevent a chemical reaction called oxidation. Oxidation can produce chemicals that are very reactive and sometimes harmful to the cells in the body. Natural antioxidants such as vitamins A, C, and E work together to prevent oxidation and therefore have a protecting effect for body cells. The potential role of antioxidants in reducing the risk of heart disease, cancers, and cataracts is currently being studied.

Can vitamins be used to treat medical conditions?

Some vitamins can have a therapeutic use also. For example, in 1955 it was found that niacin in very large doses (1.5 to 3 g per day) could decrease serum cholesterol. While it can be used for this purpose, it is important to know that side effects such as flushing of the skin, itching, nausea, and liver damage limit its use (Gillis). A physician should supervise any large-dose vitamin therapy.

Conclusion

A plan for health promotion and disease prevention includes a diet that incorporates a variety of foods, adequate fluid consumption, moderate fat intake, regular physical activity, limiting alcohol intake, and avoiding smoking. The use of supplements should be considered together with diet and exercise to meet individual nutritional needs.

vitamin

vitamin One of a number of organic compounds required by living organisms in relatively small amounts to maintain normal health. There are some 14 generally recognized major vitamins: the water-soluble vitamin B complex (containing 9) and vitamin C and the fat-soluble vitamin A, vitamin D, vitamin E, and vitamin K. Most B vitamins and vitamin C occur in plants, animals, and microorganisms; they function typically as coenzymes. Vitamins A, D, E, and K occur only in animals, especially vertebrates, and perform a variety of metabolic roles. Animals are unable to manufacture many vitamins themselves and must have adequate amounts in the diet. Foods may contain vitamin precursors (called provitamins) that are chemically changed to the actual vitamin on entering the body. Many vitamins are destroyed by light and heat, e.g. during cooking.

vitamin

vitamin Thirteen organic substances are essential to human life in very small amounts. Eleven of these must be supplied in the diet (vitamins A, B1, B2, B6, B12, C, E, K, folate, biotin, and pantothenate); two (niacin and vitamin D) can be made in the body if there is sufficient of the amino acidtryptophan, and exposure to sunlight respectively.

The word may be pronounced either ‘vaitamin’ or ‘vitamin’.

The vitamins

vitamin

functions

deficiency disease

A

retinol β‐carotene

visual pigments in the retina; regulation of gene expression and cell differentiation;

Vitamin

Medical Discoveries
COPYRIGHT 1997 Thomson Gale

Vitamin

Vitamins are organic compounds (mixtures made from living organisms like plant and animal tissue). They are generally divided into two groups: fat-soluble and water-soluble. Fat-soluble vitamins include vitamins A, D, E and K. Water-soluble vitamins are those in the B group and vitamin C.

Many people think they can improve their health by taking vitamin pills. Most medical experts believe this is unnecessary. The experts say that eating a varied diet of fresh food and exposing the skin to enough sunlight to increase vitamin D reserves (but not enough to burn the skin) should provide enough vitamins under most circumstances. In fact, over-dosing on some vitamins can itself cause disease.

Only tiny amounts of each of the 13 vitamins are needed to ensure metabolism, but these minimum amounts are absolutely essential. The continued lack of any vitamin, even in an otherwise balanced diet, usually leads
to a deficiency disease. Vitamins were discovered as scientists searched for the causes of deficiency diseases like pellagra, beriberi, and scurvy.

Vitamins and Enzyme Reactions

While vitamins are not all chemically related, they all serve a common purpose. That purpose is helping to regulate how the body converts food into energy and living tissues (metabolism). Most vitamins accomplish this by acting as enzymes. Enzymes are chemicals which encourage chemical reactions, but are neither changed by the reaction nor are they incorporated into the reactions's final product.

Many vitamins, including all of the eight vitamins in the B group, are inactive until converted into coenzymes. Coenzymes are organic substances which combine with a protein to form an active enzyme system. The human body needs vitamins to work properly. We acquire almost all of the vitamins from the foods we eat. A small number of vitamins, including biotin and vitamin K, are at least partially synthesized (created) by the body itself.

How Vitamins Got Their Names

In the early part of the twentieth century, Polish biochemist Casimir Funk studied the various "accessory food factors" that had been identified. He suggested these factors be named "vitamines" or "amine compounds vital for life" (amines are organic compounds of nitrogen). After it became clear that not all these compounds were amines, the final "e" was dropped, and the substances became known as vitamins.

[See alsoBiotin ; Vitamin A ]

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vitamin

vitamin Organic compound that is essential in small amounts to the maintenance and healthy growth of all animals. Vitamins are classified as either water-soluble (B and C) or fat-soluble (A, D, E, and K). They are usually taken in the diet, but today most can be made synthetically. A danger exists in taking too many vitamin supplements. Some are synthesized in the body. Many vitamins act as coenzymes, helping enzymes in respiration and other metabolic processes. Lack of a particular vitamin can lead to a deficiency disease. Vitamin E is important in reproduction and many other biological processes. Vitamin D helps the body absorb phosphorus and calcium. It is essential for the normal growth of bone and teeth. Existing in human skin (activated by sunlight), vitamin D is also found in fish-liver oil, yeast, and egg yolk. Vitamin C (ascorbic acid) is commonly found in many fruits and vegetables. It helps the body resist infection and stress, and is essential to normal metabolism. Vitamin B is actually a group of 12 vitamins, important in assisting the process by which energy is produced in the body (respiration). Vitamin B1 (thiamine) occurs in yeast and cereals. Another B vitamin is niacin (nicotinic acid) found in milk, meat, and green vegetables. Vitamin B12 is needed for the formation of blood cells. It is found especially in meat, liver and eggs. Vitamin A (retinol), found in fish liver oil, is important for healthy eyes. See also riboflavin

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Vitamins

Encyclopedia of Drugs, Alcohol, and Addictive Behavior
COPYRIGHT 2001 The Gale Group Inc.

VITAMINS

Vitamins are organic substances that are required in small amounts for normal functioning of the body. Lack of adequate quantities of vitamins results in well-known deficiency diseases, such as scurvy from Vitamin C deficiency and rickets from Vitamin D deficiency in childhood. For the most part, vitamins are not synthesized by the body but are found in a variety of foods, hence the need for a well-balanced diet or supplementation by taking the vitamins separately.

In the United States, daily minimum requirements for vitamins are recommended, and periodically reassessed, by the Food and Nutrition Board of the National Academy of Science—National Research Council. Some professionals advocate taking larger amounts of certain vitamins is for better health or for disease prevention or therapy. The question of whether vitamins are drugs is, in one sense, a semantic issue. Sometimes, very high doses of a vitamin can actually be used as a medication. For example, in very high doses—twenty or more times higher than needed to prevent the vitamin deficiency disease pellagra—niacin, a member of the B vitamin complex, lowers blood levels of cholesterol and triglycerides and niacin is commonly prescribed for this purpose.

It is possible to Overdose and have serious side effects from large quantities of certain vitamins, such as vitamins A and D. Therefore, taking larger than needed amounts of vitamins should be done only with the advice of a physician. Deficiencies in vitamin intake can occur under a variety of situations including poverty, dieting, or certain disease states where antibiotics or other factors reduce vitamin absorption. Individuals who drink large quantities of Alcohol, for example, without adequate attention to diet often become deficient in some vitamins, such as B 1 (thiamine), and may
require their administration to avoid serious and permanent toxicity. Prolonged serious shortages of Vitamin B 1 can cause the death of certain Neurons in the brain, a situation that leads to confusion and severe impairment of short-term memory (the Wernicke-Korsakoff syndrome).

vitamin

vitamin An organic compound that is required in minute quantities by heterotrophs for their normal health and development (hence the origin of the name, from ‘vital amino’) but which they cannot themselves synthesize. Vitamins are distinct from carbohydrates, fats, proteins, and nucleic acids. They, or their derivatives, normally have à coenzyme function and their absence from the diet or their inadequate absorption from the gut gives rise to specific deficiency diseases.

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vitamin

vitamin (vit-ă-min) n. any of a group of substances that are required, in very small amounts, for healthy growth and development: they cannot be synthesized by the body and are therefore essential constituents of the diet. Vitamins are divided into two groups, according to whether they are soluble in water or fat.

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vitamin

vi·ta·min / ˈvītəmən/ • n. any of a group of organic compounds that are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body.

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vitamin

vitamin XX (vitamine). — G. vitamine, f. L. vīta life (cf. prec.) + amineAMINE. So named because it was first believed that an amino-acid was present, the sp. being later modified in order to avoid the suggestion.

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